Added a 3rd fragment to demonstrate more about normal events and sticky-events.
- Refactoring codes on the original sample.
- Use post() to update ActionBar's title.
- Use post() to switch different Fragments.
- Use postSticky() to update StickyEvent.
- Update .gitignore and git-rm some objects.
- Added BaseFragment to demonstrate coexistence between register and registerSticky.
- Added NoStickyFragment that can handle normal event but unavailable for stickies.