Basically, drop usage of nested main loops. As has been documented in
other commit messages, we use nested main loops in ways they aren't
supposed to be used. They gave us async behavior that would block
callers, but had weird behavior in some edge cases.
Switch to having async dialogs be 100% async, requiring the user to
pass in a completion callback which is triggered after the async
action is complete.
Our use of nested mainloops is still kinda wonky and a proper solution
will take some decent effort. Deal with the fact that a main loop
might exit before the thread completes, and the thread will try to
talk to resources that no longer exist.
Despite being a known quantity, autotools is so overkill for our needs,
so let's drop it and replace it with a much simpler and easy to customize
system.
