Support overriding default hotkeys on Windows

[Flix3r]

Using the super key is optimal for global hotkeys because they generally never conflict with other apps. Sadly, they do often conflict with Windows' hotkeys, which there are a ton of, many of which most users never intend on using. Overriding them could be done using LowLevelKeyboardProc without calling CallNextHookEx when the hotkey is activated.