Create working setup for using Equake with EXWM

[emacsomancer]

As it stands, calling equake-invoke in EXWM results in a fullscreen Equake frame. Calling equake-invoke a second time hides the frame, resulting (if no other Emacs frames are open) in a blank screen from which no Emacs (and thus no EXWM) commands can be called.

So there are at least two issues here:

• making the Equake frame the right size (and floating)
• making sure that when it's hidden there is at least one other Emacs frame open