It releases the SDK and all dependencies (including React Native) to the
specified Maven repo.

This new version comes with an updated JSC runtime, so we no longer need to
depend on the updated version ourselves.

Consolidate all failure cases into a single one: CONFERENCE_TERMINATED. If the
conference ended gracefully no error indicator will be present, otherwise there
will be.

I'm ashamed to admit that I spent several _days_ chasing a bug that was already fixed. :( This obvious instruction would have been a time-saver.

Provide a default and builtin default implementation which finishes the
Activity, same as before.

What this PR removes is the ability to provide a custom default handler because
applications can already take this decision when calling `onBackPressed`. In
addition, make `onBackPressed` return `void` because it's virtually impossible
for it to return `false` (that would mean that there is no
`ReactInstanceManager`, which means there is no app to begin with).

In addition, remove the use of `BackAndroid` since `BackHandler` contains an iOS
shim now.

Due to a switch to a newer version of JSCore, the jsc-android dependency is now used by the
SDK. As this dependency is not (yet) available in the Jitsi Maven repository, an error like
this is reported when an application is ran that uses the SDK:

    com.facebook.react.common.JavascriptException: Can't find variable: Symbol

This commit primarily improves the instructions on how to create a local Maven repository
that contains all required dependencies, including the JSCore dependency that was missing.

This intends to address the issue described in https://github.com/jitsi/jitsi-meet/issues/3399

This reverts commit 9e0fee6c7d.

WebRTC requires Java 8, and Java 7 is now considered unsupported:
https://groups.google.com/forum/?utm_medium=email&utm_source=footer#!msg/discuss-webrtc/V1h2uQMDCkA/RA-uzncVAAAJ

The new libwebrtc.jar contains an extra unused class file, when proguard is enabled result in the following warning:

org.chromium.build.BuildHooksAndroidImpl: can't find superclass or interface org.chromium.build.BuildHooksAndroid

Updates react-native-webrtc to get rid of Java 8 requirement for
the Android app.

This only works automatically on Android >= 8. On other platforms / versions, it
relies on the SDK user on implementing a "reduced UI" mode and reacting to the
"request PIP" delegate method.

It was recently introduced in WebRTC, so we we need to enable it project wide.
As for what features are supportd, see:
https://developer.android.com/studio/write/java8-support.html

Based on work authored by Shuai Li <sli@atlassian.com>, Daniel Ornelas
<dornelas@atlassian.com>, and Lyubo Marinov <lmarinov@atlassian.com>.

The error is stored in the redux store in base/config so other components can
consult it. It is also broadcasted as a new event in the external API for the
SDK.

In iOS this is automagically done in the view destructor, bunt we don't have
that luxury in Java we have to do it manually.

The new disponse() method MUST be called when the Activity holding the view is
going to be destroyed, typically in the onDestroy() handler.

Introduces loadURLObject in JitsiMeetView on Android and iOS which
accepts a Bundle and NSDictionary, respectively, similar in structure to
the JS object accepted by the constructor of Web's ExternalAPI. At this
time, only the property url of the bundle/dictionary is supported.
However, it allows the public API of loadURLObject to be consumed. The
property url will be made optional in the future and other properties
will be supported from which a URL will be constructed.

Initializing a new URL/NSURL instance is a chore especially when one
takes into account that the JavaScript side (1) is loading the URL
asynchronously and (2) is capable of parsing strings that may or may not
be represented as URL/NSURL.

The Android method loadURLString(String) may have been called
loadURL(String) to overload loadURL(URL) but I didn't want to do that
because:

1. It would not be compatible with existing source code such as
loadURL(null) which would have become ambiguous.

2. I wanted to achieve better convergence with the iOS API.

Also expose this in the native SDKs.

The current implementation doesn't use the API and Transport modules. This is
due to the fact that they are too tied to APP at the moment, which is web only.

Once API is refactored and moved into the Redux store this will be adjusted,
though it's unlikely that the lowest level React Native module (ExternalAPI)
changes drastically.

This commit also introduces a stopgap limitation of only allowing a single
instance for JitsiMeetView objects on both Android and iOS. React Native doesn't
really play well with having multiple instances of the same modules on the same
bridge, since they behave a bit like singletons. Even if we were to use multiple
bridges, some features depend on system-level global state, such as the
AVAudioSession mode or Android's immersive mode. Further attempts will be made
at lifting this limitation in the future, though.

Dames en heren, welcome to Jitsi Meet SDK for Android, the Jitsi Meet library
for Android.

The Jitsi Meet SDK encapsulates React Native and all the dependencies Jitsi
Meet has so other aopplications can integrate it easily.

Unlike iOS, creating "fat" libraries is not allways (if at all) possible on
Android, however, effort was put into making the integration as easy as
possible.

While React Native can be embedded in native applications, I don't think it was
designed to be embedded as part of an Android library, hidden away from the
application using it. This surfaced as a number of issues which had to be
addressed specifically due to our use-case:

- Activity lifecycle methods must be linked with the React Native engine, so the
  library provides wrapper methods.
- Custom fonts have to be manually added as assets, since the provided gradle
  script doesn't work properly in a library target.
- The RN packager has to be manually triggered since the gradle script will no
  longer do it for us.

At this stage, the Jitsi Meet application is just a small single activity
application which uses the Jitsi Meet SDK to create a single activity which
represents the entire application. Events and external conference handling are
forthcoming.

PS: Yours truly would like to add that it was a lot more fun to work on the iOS
side of things.