Create a new status manager that's built in glade

Behavorial Changes:

* Confirmation dialog for remove has been removed.
* Remove button is disabled if the currently selected status is the active
status. Previously this scenario was silently ignored after confirmation.

Errata:

It is possible to open multiple modify windows for a status. Previously the
editor was reaching into the manager and controlling this pointer. I was going
to fix this, but the editor isn't a widget yet and I don't like doing duplicate
work.

Testing Done:
Basically tried everything I could think of with editing and selecting and so on.

Bugs closed: PIDGIN-17590

Reviewed at https://reviews.imfreedom.org/r/1322/