gnome-shell-manager: Honor ignore autorepeat grab flag

Keep firing action until accelerator was released unless accelerator was grabbed with "ignore autorepeat" set.

Enums grabbed from mutter (src/meta/prefs.h) as of commit 1a4f03bd79a2ba502dbd6a932ec20a73921d6709

One step towards fixing #525 (closed)

Draft because this needs some testing