Improve connectivity error handling & reporting

[atsakiridis]

Impacts:

1. When connectivity is lost during ongoing call:
   • Show to the user what happened (right now nothing is shown to the user)
   • Make sure that on such event the UI is updated quickly
   • Some times after connectivity is lost we might get a timeout. Remember that ice failure triggers signaling disconnect, which would probably timeout as well (i.e. taking 32 seconds which is a lot). But apart from that seems that the time out takes even more than 32 secs + 5 secs (around the time for ICE to fail when without connectivity), so we need to investigate the whole behavior on event of connectivity loss, as it's something VERY common.
2. When Restcomm Connect returns 403 to an outgoing call or BYE with reason header display that issue in the UI so that the user gets a hint on what is going on.
3. See if there's a media issue like cannot establish media due to connectivity checks failing, if we can clearly indicate that

Check @deruelle 's TestFairy sessions for more info: session 1, session 2, session 3

[atsakiridis]

Moving it back to 1.0.0.BETA5 from 2.0.0, as it is pretty important for the Restcomm Cloud