ContactsList

**update:**
1. modified a google contact provider to load and search contacts on the phone;
2. instead of using `DialogFragment`, add `slide_in_bottom/top` actions for contact list as mock-up of facebook messenger.

**issue:**
1. need click back icon once in order to have search contact ability work properly.

**to-do:**
1. add multiple selection on contacts;
2. add `TimePicker` to schedule Date/Time;
3. send invitation to selected contacts.