Random coding style-related issues that bothered me while reading the
source code touched by "Fix local video disappearing from local
thumbnail" (https://github.com/jitsi/lib-jitsi-meet/pull/571). These
include naming, formatting, comments, typos, duplication.

Commit "fix(JitsiLocalTrack): restore 'inMuteOrUnmuteProgress'" removed
all read occurrences of dontFireRemoveEvent so the one and only write
left is now obsolete.

Flag 'dontFireRemoveEvent' was unreliable, because if
the JitsiLocalTrack is muted/unmuted rapidly it's state can be false
at the time when ended event is triggered. The event handlers must be
unregistered to handle this gracefully.

Restores 'inMuteOrUnmuteProgress' flag used by the LocalSdpMunger.

(cherry picked from commit 2e6c4dd)

fix(JitsiConference): reduce verbosity level

There are scenarios when it's ok to call setP2PStatus again with
the same value. For example when P2P is stopped, before it starts with
the A/B testing mode enabled. It's only important to know that it
happened, but it's not an error, because the code will not execute
and return immediately.

* feat(quality-slider): expose video constraint method and data channel opening

* squash: rename to data channel opened

'echoCancellation' should be disabled by 'disableAEC'
'disableAP' should disable all options

Instead of failing with an error if another operation is in progress, which is
impossible to know as a user, chain them using the primises API.

fix(JSPC): local tracks not advertised

fix: never miss 'ondatachannel' event

Moves the call to 'setLocalDescription' from 'sendSessionInitiate' to
'invite' as it was easy to overlook.

In case when the answer is being set for the first time, full sRD/sLD
cycle is required to have the local description updated and SSRCs
synchronized correctly. Otherwise SSRCs for streams added after invite,
but before the answer was accepted will not be detected. The reason for
that is that renegotiate can not be called when adding tracks and they
will not be reflected in the local SDP.

The 'ondatachannel' even listener must be set as soon as
the TraceablePeerConnection is created and before the offer is accepted.
We've observed situations where the ondatachannel event was missed,
because the listener is bound too late from the JingleSessionPC
'acceptOffer' success callback.

Send resolution (in pixels) to the analytics backend.

As new use case for joining a conference without calling GUM has been
added to jitsi-meet enumerate devices should not be delayed. In fact not
only it was delayed, but never called in such case
(getUserMediaStatus.initialized stays false forever).

Fixes crash on undefined var in case get user media was not called,
before the conference started.

* make audio processing constraints configurable

AP: echoCancellation is a "master switch" for disabling all audio processing.  set to disableAP=true and stereo=true allows fullband, stereo sound.
AGC: misbehaves with certain 'pre-gained' mics.
HPF: can't hear any effect but it's the last constraint to make configurable.

* Update RTCUtils.js

Start screen sharing

If we detect a custom <ignore tag in presence unavailable we ignore those presences and do not process them.

* add support for signaling simulcast for unified plan

1) munge the incoming offer to advertise support for receiving simulcast in unified plan
2) add 3 simulcast encodings via rtp sender
3) inject an ssrc-group line, even when using rids for simulcast (jicofo will rely on this)

* add rid information to the session-accept jingle

* address lenny's feedback

* make firefox simulcast configurable

* fix missing comma

Will trigger external installation also for sites that are not the main
whitelisted domain. This allows to reuse one extension for many sites
(they still have to be on the whitelist, but only one can be "main").

Will not crash, but delay requests if arrive, before the initialization
process is done (there is no way to tell that really).

CHROME_EXTENSION_USER_GESTURE_REQUIRED will be triggered if
the extension installation fails, because the request to get desktop
stream did not originate in user gesture handler (a button click for
example).

* feat: add 'disableDesktopSharing' option

* ref(ScreenObtainer): simplify init

add method to send a receiver video constraint message

Treats local/remote relayed addresses differently.

Due to it being ran asyncronously, it's possible a replaceTrack operation is
scheduled while there is a valid PC, but by the time it runs was closed.

Accommodate to this situation by pretending everything is just peachy.

fix(JitsiConf...): stop P2P on JVB121

The P2P session must be stopped with '_stopP2PSession' once accepted.

Remote control

Fix when P2P disabled in config