Fix error handling
End the application when the window is closed
Explain what each error means
Commit current state of affairs

It's been a _long_ time. Before we move on, commit what we have so we can
easily revert if needs be
Refactor

While I was procrastinating over gjsjoystick, someone introduced
something called "gjs", a binding for GObject in JavaScript stuff.

Rename to libjoy instead. Not only allows this us all kinds of
interesting puns like "I just released joy" etc, it also makes for a
more compact API: joy_stick_new() rather than gjs_joystick_new()...
Updates

Things working:
- axis/button events
- autopluggin of joysticks in the model
TODO: clean up properly so that if a joystick is removed and then
reinserted, we don't get a segfault.