:white_check_mark::apple: Allow Ctrl+C to only start command mode on Mac

Add requirement of .platform-darwin to Ctrl+C entering command mode.
Add helper to mock platforms in tests
Make Ctrl+C test mock platform-darwin before testing
Make keybinding more specific to match current style

Add .editor when checking if command mode has been activated
Merge pull request #339 from sgtpepper43/master

Restrict Command Mode Activation with Ctrl+C to Mac only