* ref(JSPC): rollback doRenegotiate

Modify the code to the old strategy without shared 'doRenegotiate'
method.

* ref(JSPC): add/remove duplication

Removes duplication between add and remove remote stream methods.

* fix(JSPC): remove Timeout

Removes wait timeout for remote stream added/removed. It should not be
necessary given that the task executes on the modification queue and
the initial offer/answer should execute before
'source-add'/'source-remove'. Jingle 'session-invite'/'session-accept'
is sent, before any other notifications.

* feat(JSPC): verify SSRC changes

Will print an error if there was change to local SSRCs where it should
not happen (video mute on browsers where video stream is disposed on
mute).

* fix(JSPC): not always renegotiate

When adding/removing tracks as mute/unmute it only makes sense to
renegotiate if the initial offer/answer cycle has already been executed.

* ref(JSPC): remove duplication

Removes duplication around add/remove as unmute/mute.