Install and preference mode for Mojito.app

[fangpenlin]

For most of input method out there, they are installed via installer. Input methods in OSX, they are all actually App, but they lives in ~/Library/Input Methods, also, you need to call some system API to register it if I recall it correctly. To bring good user experience, I think maybe we can try to let Mojito.app to determine whether we are running under ~/Library/Input Methods as an input method or executed as a stand alone app. If we are executing it as a standalone app, we provide install view and preference view.