Add operator to register and remove keybindings

[NathanLovato]

Add 2 operators, accessible from the add-on, preferences, to register and unregister keymaps.

• parse keymaps from a dict (and/or a JSON file?) for easier editing
• duplicate the active keymap, rename to Power Sequencer
• register and replace existing shortcuts if need be
• Print collisions to the console
• Report to the user?
• add buttons to the add-on prefs

Should there be an option to register the full keymaps or by operator type (e.g. markers, editing, etc.)?

[NathanLovato]

How should the add-on handle keyboard shortcuts? A lot of Blender add-on force their keymaps, even brute delete other add-ons' mapping every time blender starts and honestly mess up your profile.

At the same time, downloading a pre-made shortcut scheme means if you want to customize yours, you've got to start over every time a new version comes out, or to port your changes.
Power Sequencer changes a lot of mappings, including some default ones. So:

1. Should we stick to a predefined keymap file?
2. Should there be buttons to e.g. create a copy of the current profile with new keyboard shortcuts from the add-on in the prefs?

[doakey3]

This feature has been added with 9c51d25

[NathanLovato]

Thank you very much, let's close the issue for now then :)