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
Merge pull request #213 from aBothe/pr3

Handle possible NullRef/JsonSyntaxException in Drop.deserialize()