Allow both custom and addons/themes keyboard shorcuts

[twitwi]

Is your feature request related to a problem? Please describe. When an addon (or probably theme) defines keyboard shortcuts and the presentation author also wants to define custom shortcuts, the addon shorcuts are ignored. Similarly (probably), only one addon can contribute keyboard shorcuts.

Describe the solution you'd like It would be nice if the shortcuts were merged. And ideally, when a key is bound both in the addon and presentation repo, the later should be used.

Describe alternatives you've considered It is always possible to (manually) "eject" and merge the addons shortcut.