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.