Make numlock state on boot configurable
This will expose 3 settings for numlock behavior:
1. Numlock is off on boot (this is the current default behavior)
2. Numlock is on on boot
3. Numlock will restore the state from the last boot
Fixes#369
* Address comments:
Get keyboard after create_seat called rather than returning from
create_seat.
Use constants rather than magic numbers for keypress.
Only save updated modifier state after keypresses are handled/skipped.
* Remove unused import, fold other into existing use block.
