Add basic gradle compilation script

Make the project compile with SDK 21 (lollipop)

ContactList: Separate creation of ContactListAdapter and managment of the group list This is two separate things. getContactListAdapter is called in ContactListFragment.onActivityCreated() which is during a fragment transaction. Management of the group list calls FragmentPagerAdapter.notifyDataSetChanged() which repopulate the FragmentPagerAdapter and to do so calls FragmentManager.executePendingTransactions() in a recursive way and is not allowed (IllegalStateException).