When in PiP mode the LargeView will not be large enough to hold the avatar (for
those interested in the details, our avatar's size is 200, and in PiP mode the
app is resized to about 150).

In order to solve it, this PR refactors how the avatar style is passed along,
reducing it to a single "size" prop. With this only prop, the Avatar compononent
will compute the width, height and borderRadius, plus deal with some Android
shenanigans.

In addition, the LargeView component now uses DimensionsDetector to check its
own size and adjust the size prop passed to the Avatar component as needed.

The video will switch to the avatar and be tinted with gray. On the large view,
a text message indicating the user has connectivity issues will be shown.

Prepare for React 16.

Refactors the previous "[RN] Cache avatars and provide a default in
case load fails" for the purposes of simplification but also modifies
its functionality at the same time. For example:

- Always displays the default avatar immediately which may be seen if
  the remote avatar needs to be downloaded.
- Does not use random colors.
- Uses a default avatar image which is not transparent and ugly but at
  least it's the same image that's used on Web. I've started talks to
  have images/avatar2.png replaced with a transparent and beautiful
  so that will land later on and we'll see the automagic colors in all
  their glory then.

The files styles.js are used (pretty much) on React Native only and each
of them exports 1 name. Export it as default to cut down on source code.

When entering audio-only mode, VideoBridge is instructed to stop sending
remote videos. However, if the instruction fails because DataChannels do
not work, for example, then the app continues to display the remote
videos. Even though they're received in the case of such a failure, no
videos are to be displayed in audio-only mode.

They better represent if a participant has video available or not. There are
cases when even a participant in the last N set would not have video because it
disconnected momentarily, for example.

Until we make a decision on access modifier hints and adopt a respective
coding style, consistency is king.

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.