Update to the latest version of dependant libraries and tools.

SDK version stays at 19 to avoid bringing in Wear / Material Design themes
which are not handled well.
Prepare for release 1.2.0-beta-1.
Use equals() instead of == when comparing songs.

Fixes bug where the song was always considered to be different.

(cherry picked from commit d5318de40a9165bd20baf80e97888dae7933b659)
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.
Check for a null getPlayStatus() response.

Annotate the response as @Nullable, with Javadoc that explains why.
Prepare for release 1.2.0.
Merge branch 'release-1.2.0' into develop

* release-1.2.0:
  Prepare for release 1.2.0.
  Check for a null getPlayStatus() response.
Update the feature graphics for 1.2.0 release and the light theme.
Add screenshots and icons for the Amazon market.
Merge branch 'lint' into develop

* lint:
  Mark some variables that can be private and/or final as private and/or final.
  Compile the regex patterns for string splitting once, not on every split.
  Remove unused 'activePlayer' variable.
  Remove unnecessary test, serviceConnection is never null.
  Use "string".equals(object) instead of object.equals("string") to avoid potential NPEs.

Conflicts:
	Squeezer/src/main/java/uk/org/ngo/squeezer/framework/ItemListActivity.java
Always try and order pages, catching HandshakeNotCompleteException as
necessary.

The previous code could crash if the handshake had completed at least
once in the activity's lifetime.

Rather than try and track the handshake status in the activity, catch
the exception and try again in onHandshakeCompleted.
Fix null pointer exceptions when updating the ongoing notification.

- Refactor the scrobbling code in to Scrobble.java.

- Check that objects are non-null before operating on them.
Remove duplicate entries from the release instructions.
Prepare for release 1.2.1.
Merge branch 'release-1.2.1' into develop
Merge branch 'develop' into lint