Add window maximize capabilities.

This would allow a window to take up as much screen space as possible without going into full-screen mode. If it works out, this fixes issue #64.

- [x] Added UI items for new hotkey recorder.
- [x] Added new maximize action.
- [x] Integrated new maximize action into `calculateWindowRect`.
- [x] Add default shortcut to plist. (Not sure on the best choice, but there's a placeholder there now.)
- [ ] Anything else I may have missed.
- [ ] Any testing that needs to be done to confirm this doesn't break any existing functionality.