This is inspried by the Gio.ActionEntry struct, which I can't figure out
how to get working in Python. I add on a few extra helpful features,
such as:
- Automatically creating a Gio.SimpleAction
- Tracking the desired accelerator keys
- Binding the "enabled" state to a specificed property at construction
Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>