Feature Update

1. Set up a basic tab controller as the initial entry;
2. Set up a navigation controller to handle the events part
3. Set up a table view controller for events list as the root view of
navigation controller;
4. Config the data source of table view(local json file);
5. Set up a view controll to display to details of event;
6. Rearrange the segue and corresponding preparation;
7. Some UI stuff s.l. tab icons.
8. Something more but i cant remember now…
9. Some verification of the possibility that fetching data from web
service directly and update local data records.
10.  Some test case that shows the inconvenience and unnecessity of
using core data for this app.(Orz..)

Known Bugs:
1. Leaving the root view of navigation then switching to other tabs and
back, it will not pop back to root view automatically.