Adding View pager support for HomeActivity.

- Added a view pager of two Pages. HomeListingsFragment and UserFragment.
- Refactored UserProfileFragment to UserListingsFragment. We no longer need to hide and unhide TopCardFragment.
- Updated TopCardFragment and UserListingsFragment to be created using the userId given when instantiating. This
  will help in creating User pages for any user in future.
Merge pull request #22 from Hawk-It/add_view_pager

Adding View pager support for HomeActivity.