Fixed bug in DropController.retrieve() where a special state led to a drop message be handled twice or more times. #200
Handle possible RuntimeExceptions that are likely to be caused by invalid Json syntax.
If this wasn't handled, consciously injected errornous JSON could crash the entire client.
Corrected DropController.decryptDrop() javadoc
Introduced deserialization tests for invalid/illegal JSON syntax in drop messages
Added rationale comment to DropController.retrieve() why InvalidKeyExceptions won't be handled
Pass DropController.sendAndForget() exception to logger for better stacktrace analysis
Pass exception in DropController.handleDrop() to logger
Merge pull request #213 from aBothe/pr3

Handle possible NullRef/JsonSyntaxException in Drop.deserialize()
Merge pull request #212 from aBothe/pr

Fixed DropController.retrieve()-Bug; Improved exception logging