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

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

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

Make sdp munging logic for changing codec preferences more generic
Do not negotiate High profile H264 codecs on when RN clients are in the call

Fixes random tests failures after frameworks upgrade.

* exclude fec-fr secondary ssrcs when looking for primary ssrcs

this was causing us to generate an rtx ssrc for the fec stream

* fix variable

add a multi-codec test case for preferCodec

* re-enable setting for enabling/disabling rtx

* add tests for rtxmodifier.  (and a bugfix found by the tests)

* remove rtx handling from sdp-consistency (it will be handled separately)

* better error printing in JingleSessionPC around renegotiation

* add rtx modifier to handle inserting local rtx ssrcs, keeping local rtx ssrcs consistent, and imploding remote rtx ssrcs

* jsdoc, es6 cleanup, logging tweaks

* fix line that's too long

* add a 'parseGroupSsrcs' helper function

* fix a bug when passing group ssrcs to be parsed

* address pr feedback

* address pr feedback

* fix for loop

* address pr feedback

* better const in SampleSdpStrings