Add convenience abstract super classes

@ReceiverAction and @ServiceAction require to add an empty
implementation of the corresponding event handling method, since the
method is abstract in the super class. For convenience, we provide
AbstractBroadcastReceiver and AbstractIntentService classes, which
implement the corresponding method, so the client does not have to.
Merge pull request #1255 from WonderCsabo/1239_convenienceAbstractApiClasses

Add convenience abstract super classes for @ReceiverAction and @ServiceAction