* feat(toolbox/native): custom buttons for the OverflowMenu

This event is the event host applications need to listen to for knowing when to
dispose the SDK from now on.

Since the introduction of breakout rooms it's possible that we navigate from one
meeting to another, so there will be several conference join / terminations.

In addition, local track destruction is now moved to SET_ROOM when there is no
room, aka, we are going back to the welcome page or to the black page.