leaving a MUC before joining it was a work around for servers that did not treat a
<x/> join as a full join and didn’t send the full user list if they thought the user was
still in the room.
this happens if Conversations restarts after an inproper disconnect. The MUC will think
the user is still in the room.

however nowadays most modern servers will treat <x/> joins as full joins. on the user hand
leave before join would trigger flood prevention on ejabberds and race the first message
with the actual join (making the message arrive before the user is considered in the room)

we don’t want 'manage accounts' and 'settings' to show up when within a conversation.
we also move out disable notifications and add to favorites into an overflow overflow
to make the menu shorter (after adding 'Search messages' it became very crowded)

Conversations would attempt to feed any candidates found in the session-accept into
WebRTC; even if the session wasn’t setup correctly.

this commit processes the candidates only if the session was setup correctly

fixes #3867

fixes #3854

fixes #3849

fixes #3847

JingleRTPConnection shuts down the WebRTCWrapper before transitioning into a terminal state.
(This allows us to make sure it is actually closed when reaching that state);
However that means that, when we get a UI redrawn inbetween closing and transitioning we might
still be in SESSION_ACCEPTED but with no PeerConnection. This traditionally has triggered
an IllegalStateException on getting the EndUserState.
This commit catches the ISE and returns 'ENDING' instead.
Chances are that this is only visibiliy for a very brief time in the UI before the transition
triggers the UI to redraw with the proper state.

fixes #3848