Implement interface for adding handlers to MediaStreamTrack object

Device selection rework

Moves caching of selected endpoint out of data channel.

fix(start_muted): Fixes start muted feature

Always saves password as we can make several room join attempts.

fix(xmpp.js): User id format

Fixes desktop sharing.

Fixes resolving this when passing function after enabling es6.

This currently fixes problem for participants joining in a room with other participants and trying to send initial value of selected local participant will throw an error. And fixes a potential problem if the UI can select participants before their video is available, before session initiated, can make local state with jvb inconsistent. Also if we want to have multiple selected endpoints or pinned participants and this is done before session-initiate caching should be done before creating data channel (currently selecting multiple is not possible).

Fix createConnection broken in 9781a0d

The places of the two arguments of the function createConnection were
switched in the function definition but the call to the function
remained unchanged.

ES6 for modules/xmpp/xmpp.js and it's related files

ES6 for JitsiParticipant

ES2015

ES6 for JitsiTrackError

ES6 for JitsiTrackEvents

Adds a option to set custom callstats script.

Enable ES6/ES2015

Handle session-terminate

Use 'sendToAll' for 'session.restart' and 'session.terminate' events.

Moves analytics event for feedback to the library.

Enable lipsync by default + fixes