Using a dialog after username and password have been provided.

So IDNs are not rejected. Invalid server names will be caught later.

We explicitly set a parent. We can't assign to
ApplicationWindow.transientParent though, only to
Window.transientParent, so we just call setTransientParent in C++.

fixes #636

Co-authored-by: DeepBlueV7.X <nicolas.werner@hotmail.de>

Why didn't I see these earlier?

RIP

There are probably a few things wrong with this, but I'm going to call it good enough for an initial commit

Also fix a lot of warnings.

Nested QEventLoops are scary. Ultimately we shouldn't use them, but I
have no better solution right now.

fixes #656

might fix #656