* fix(sdp): provide SCTP streams, because the XMPP parser expects them

* fixed linting error

This PR switches to generating sctp-port based SDP.
It also adds support for parsing sctp-port, but can handle
fallback to old-style sctpmap as well.
Fixes: #1778

the protocol was switched back in Chrome 44 in 2016:
  https://bugs.chromium.org/p/webrtc/issues/detail?id=2796
the port switch more than five years ago too.

...to advertise track's muted state and the video type.

For now, if the source name signaling flag is enabled, both legacy and
new <SourceInfo> element will be used at the same time. This is to be
able to interoperate with legacy clients and start testing the new
format at the same time. Whenever possible <SourceInfo> will be used
as main source of truth with the fallback to legacy <audiomuted/>,
<videomuted/> and <videotype/> elements.

The issue was caused by incorrect ordering of the mixedmslabel mline.
sdp-interop is expecting that this mline was the first one but in
reality we were placing it last. This was causing the direction of a
user related m line to be sendrecv instead of sendonly. In certain
situation this issue was causing 2 MediaStreamTracks associated with a
single MediaStream/participant.

This is the first step in adding support for multiple
streams per endpoint. Each source(stream?) needs to have
an identifier. For now always generate the 0 index name
until the machinery for sending more than 1 stream is put
in place.

* send only MSID attribute

* add feature flag for source name signaling

* log a msg if source name signaling is enabled

This fixes an issue where the bridge doesn't forward the HD stream from Firefox to other users in the call. The order of the ssrcs produced by the browser is from Highest resolution to lowest whereas the bridge assumes it to be from lowest to highest as is the case in Chrome and Safari.

... is stopped. If there's any sRD/sLD cycle happening
while the screen sharing stops, the local track
returns muted and it was injecting fake video SSRCs
which results in invalid SSRC description.

At the time when it happens there's error log in jicofo:
"Error adding SSRCs from X"
and the client will get bad-request error in response
to the source-add request.

Hurts mobile performance. They can still be enabled by setting the level at the
right value (debug / trace).

In unified plan, re-use of m-line (i.e., adding an SSRC, removing it and then adding it back) causes the browser to not render the media on Chrome and Safari. The WebRTC spec is not clear as to how browsers have to behave, this doesn't cause any issues on Firefox. As a workaround, only change the media direction and leave the ssrc in the remote desc. This automatically triggers a 'removetrack' event on the associated MediaStream and the track can be removed from the UI.

Avoid configuring the encodings on chromium immediately after replace track since the encoding params are read-only until the renegotation is done.

This is needed only for JVB connections. Add unit tests for LocalSdpMunger.

If the msid attribute is missing, then remove the ssrc from the transformed description so that a source-remove is signaled to Jicofo. This happens when the direction of the transceiver (or m-line) is set to 'inactive' or 'recvonly' on Firefox. Not signaling these source updates creates issues with remote track handling on the other endpoints in the call.

Get the correct media type when generating the source identifier.

When a msid attribute is missing in the 'a=ssrc' line, use the local endpoint id as an indentifier. Move this generation logic to LocalSdpMunger. Also suppress notifying Jicfo of a ssrc change on Firefox when the change is a result of the media being suspended on the jvb connection.

Get rid of noisy logs related to SDP transformations which are redundant. Fix formatting and add missing information.

In certain cases, when RTCPeerconnection#addTrack is used, the browser doesn't produce the streamid in the 'a=msid' line which is being used by Jicofo as a unique identifier for the associated ssrc. Whenever the msid is missing in the local description, generate an ID using the local endpoint id.

SDP utility classes are spread across RTC and XMPP directories now, moving these class files to a 'sdp' directory.