Fix a bug where the UI was not updating when returning to some activities.

It was possible to get in to a situation where the service binding had
happened and the handshake had not completed. Attempts to e.g. fetch
album artwork URLs, or order information from the server in this period
would fail. This manifested as e.g. returning to SongListActivity from
another application and the album artwork and track details disappearing.

Fix by:

- Adding a HandshakeNotCompleteException to the service, thrown by methods
  that require the handshake to have completed.

- Changing ItemListActivity to request pages ordered before the handshake
  completes, not just before the service binding completes.

- Changing NowPlayingFragment and SongListActivity to update the UI after
  the handshake completes.

Fixes https://code.google.com/p/android-squeezer/issues/detail?id=79.
Update to Gradle 2.2.1.
Prepare for release 1.2.0-beta-2.