This helps the Window Manager decide how to display the window

- Don't clear the search entry when pressing the global search button
- Start a search automatically after pressing the button

When we are connected to the server we need to set some things up
before we send our initial available presence. The new state makes
it possible for other code to difference between when we are connected
and when we are available.

For example other code should not send a presence before we requested
the roster.

Fixes #9983

- Show reason when group chat is gone
- Follow redirect if one exists

- Use everywhere disco_muc()
- Cache results with set_last_disco_info()
- Raise muc-disco-update event after every successful disco
- Raise muc-join-failed when disco is not successful before join