Implement Context Keys & Conditional Keybinds

[benceruleanlu]

Todo

• [ ] Allow assigning a single keycombo to multiple keybinds
• [ ] Unify copy paste functionality into context key system
• [ ] Implement regex match operator and 'in/not in' operators
• [ ] Figure out how to handle extension authors possibly stomping context keys

Future

• Document available condition keys
• Allow user to edit the condition
• Show condition in keybinding panel

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Closes #1595 and #1089

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