Simplify the source code (with the idea that source code which does not
exist does not have to be maintained).

Additionally, apply modifications to have the source code comply with the coding
style.

Overall, prepare saghul:audio-mode for merge into jitsi:master.

It's fired before creating the conference with lib-jitsi-meet.

Recently, we reimplemented the Welcome page in React. Unfortunately, we
broke the checkbox that enables/disables the Welcome page and it would
allow checking but wouldn't allow unchecking.

Recently, we reimplemented the watermarks in React. Unfortunately, we
didn't take into account film strip-only mode.

Additionally, we duplicated watermark-related source code on the Welcome
and Conference pages.

A bug was discovered in d17cc9fa which would raise a failure to push
into the browser's history if a base href was defined. Fix the failure
by removing react-router. Anyway, the usage of react-router was
incorrect because the app must hit the server infrastructure when it
enters a room because the server will choose the very app version then.

React Native provides Platform.

Redux actions which represent "commands" should be imperative, and those
representing events should use the past tense.

This prevents the keyboard from showing up right when the app opens.