* feat(analytics): move to React

The analytics handlers have been moved to JitsiMeetGlobalNS, so now they are
stored in `window.JitsiMeetJS.app.analyticsHandlers`.

The analytics handlers are re-downloaded and re-initialized on every
lib-jitsi-meet initialization, which happens every time the config is changed
(moving between deployments in the mobile app).

* Adds legacy support for old analytics location.

Over time features/base/util became a bucket where people seemed to dump
just about anything they couldn't think of a better place for. That's a
trend I don't like encouraging. Given that roomnameGenerator.js is
currently used in features/welcome only, I'm fine with moving it there
for the greater good.

I don't like the file/function name, I'm not excited about the
complexity of the logic it implements, and it's definitely a reusable
piece worthy of being called a utility.

React Native provides a Platform abstraction which React does not
provide.

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.