This reverts commit c9a29153dd.

Now that react-native-webrtc supports the permissions system in 23, use it since
it provides a more pleasant experience to users.

In addition, fix a bug in the previous code: the React Native view must be
loaded after we have acquired the permission to draw on top of other apps,
otherwise our app may crash while we accept the permission, since React may try
to draw.

It must match the major number in buildToolsVersion.

API level 22 is below 23 (aka Marshmallow), which included an overhaul in the
permissions system. React Native recommends 22 (it's the default when you create
a new app) and there have been reports when set higher [0] and [1].

This also fixes a critical bug, wherein Jitsi Meet wouldn't request permissions
for the camera and microphone.

Last, this change also allows us to get rid of the overlay checking code,
because it was only needed for API level 23 or higher.

[0]: https://github.com/facebook/react-native/pull/10479
[1]: https://github.com/facebook/react-native/issues/10587

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.

Recent versions of the Android plugin for Gradle started to automatically
download the SDK build tools dependency if it is not installed already.
So it is no longer necessary to have the developer of the Android app
install the SDK build tools dependency in advance.

As a step toward merging jitsi-meet-react with jitsi-meet to share as
much source code as possible between mobile and Web, merge the part of
jitsi-meet-react's source tree which supports mobile inside the
jitsi-meet source tree and leave jitsi-meet-react's Web support in the
source code revision history but don't have it in master anymore because
it's different from jitsi-meet's Web support. In other words, the two
projects are mechanically merged at the file level and don't really
share source code between mobile and Web.

As an intermediate step on the path to merging jitsi-meet and
jitsi-meet-react, import the whole source code of jitsi-meet-react as it
stands at
2f23d98424
i.e. the lastest master at the time of this import. No modifications are
applied to the imported source code in order to preserve a complete
snapshot of it in the repository of jitsi-meet and, thus, facilitate
comparison later on. Consequently, the source code of jitsi-meet and/or
jitsi-meet-react may not work. For example, jitsi-meet's jshint may be
unable to parse jitsi-meet-react's source code.