* 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.

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.

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

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

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.

Old config.js versions don't have the p2p property.

This commit changes the way the average stats are being reported to the
analytics backend. Instead of prefixes for the different scenarios
("p2p_", "jvb121_" and no prefix for multi-party calls) we now have
properties that allow to distinguish which scenario an event pertains
to. The query language of the analytics backend can be used to build
appropriate queries that group by those properties.

Additionally, we now report whether the average stats event concerns a
relayed call (a call that's routed via a TURN server) or not.

They are really verbose, and add no real value. In addition, log the channel
type once opened.

* ref: Moves the deployment info variables to config.js

instead of using globals.

* feat: If configured, adds the user's region to presence.

* fix: Guards against accessing undefined properties,

and uses the crossRegion variable from the config.

* style: Fixes formatting.

Until we have a default config template, make sure we default to having P2P
enabled.

Also add a preferH264 option for P2P.

Some browsers may not support data channels (hi there, Edge!) and sometimes it
may not be desirable for other reasons.

* ref(JSPC): simplify SSRC owner in P2P

There's no need for any extra extensions for SSRCs owner signalling in
P2P, because it's always the remote peer who owns them.

This also fixes a problem where no SSRC owner was added for 'source-add'
in P2P (for JVB conference Jicofo adds that).

* fix(TPC): always advertise 'sendrecv'

Our media direction is only ever updated on the remote side with
the initial offer (or answer). Because of that we want to advertise
'sendrecv' even if we start with no video (or audio) track.

It is OK to adjust this direction in the localDescription getter,
because it's adjusted again in the setter to the correct value based on
local tracks, so the SDP transformation chain still works fine.