Knowledge is power, man!

The config.js cache predates the feature base/known-domains.
Technically, it's also able to recall more domains that the feature
recent-list can (because the latter limits its entries).

With this the RN component and the consumer app can share same CallKit
provider, configuration, and enable to be part of multiple listeners of
the CallKit flow events. The main driver of this is to enable the
consumer app to be able to report an incoming call to the OS before
loading the JitsiMeetView. Once the user answers the call, the app can
instantiate a JitsiMeetView, pass the CallKit call UUIID, and the Jitsi
Meet components will handle the connection and report back to CallKit
that the  call has been established.

Moves the things around to be able to override the config with the URL
params specified in the hash part of the location URI to which the app
is navigating to.

* feat: Whitelists the gatherStats option.

* doc: Replaces obsolete disableStats option with gatherStats.

* Removes unused config logic.

* Whitelists config options that can be overridden using the URL.

* Recorder login with credentials, not supported by externalconnect.

Jibri uses xmpp credentials to login, which is not supported by externalconnect, so we want to skip it till that is supported.

* Whitelist only config.js

* Extracts whitelisting in separate function.

* Javadoc introduced @code as a replacement of <code> and <tt> which is
  better aligned with other javadoc tags such as @link. Use it in the
  Java source code. If we switch to Kotlin, then we'll definitely use
  Markdown.

* There are more uses of @code in the JavaScript source code than <tt>
  so use @code for the sake of consistency. Eventually, I'd rather we
  switch to Markdown because it's easier on my eyes.

* Xcode is plain confused by @code and @link. The Internet says that
  Xcode supports the backquote character to denote the beginning and end
  of a string of characters which should be formatted for display as
  code but it doesn't work for me. <tt> is not rendered at all. So use
  the backquote which is rendered itself. Hopefully, if we switch to
  Markdown, then it'll be common between JavaScript and Objective-C
  source code.

Iterate over objects and copy over primitives and arrays
instead of using _.merge, as merge will not replace a config
entry completely. For arrays in a target object, the arrays
will have its indices replaced. This means if a source array
is empty, the target array will be left alone. Similarly,
if the target array is longer than a source array, there
will be indices not touched in the target array.

This makes it possible for the following URL params to work:

config.p2p.enabled=true&config.p2p.preferH264=true

Make 'Add jwt module to react' work on mobile.