Masked hotkey fix

Reviewers, please review and merge https://github.com/CleverRaven/Cataclysm-DDA/pull/7291 before this. This PR shares most its commits with that one, so once it is merged, this PR will be easier to review.


This is based on top of https://github.com/CleverRaven/Cataclysm-DDA/pull/7291, which isn't merged yet. The only new commit here (that isn't in https://github.com/CleverRaven/Cataclysm-DDA/pull/7291) is https://github.com/lucianposton/Cataclysm-DDA/commit/362549cbe3a79a5b2d82d77ca199b993d59cb154

If a user adds a local hotkey that masks the default hotkey, removing the hotkey results in unexpected behavior. That hotkey will enter a state where only local hotkey keybindings can be added -- the user is unable to return the hotkey back to its original, default state (it shows up highlighted in green and can't be reversed).

This patch treats user created local hotkeys specially. If keybindings of a user-created, local hotkey are removed, that hotkey is deleted, reverting back to the hotkey in the default context.