More complete Ace-style key binding and Mac-style key symbol display support

The following features are added:
1. Convert keys between Windows and Mac
2. Automaticly convert "Ctrl" in keys.json to "Command" on mac,  use "MacCtrl" to present "Control" key on Mac.
3. Use Ace-style key definition and works with default Ace key bindings.
4. Mac-style shortcut symbol display.

It works on Mac, please test on other platform.