Invitation Fragment

1. fragment that contains base layout, haven't put date&time in yet
2. multiple selection of listview
3. the action bar button in RestaurantDetailActivity now launches dialog
4. added a static method in ParseClient that overloads getMyFriends, can take a callback class as parameter

TODO:
1. add date&time, and possibly location
2. compose JSON, send push notification
3. enhance the creepy UI of the fragment