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
Implemented multi sub-key support

Old getter are marked as deprecated. They will be removed when all other
methods have been changed to the newly returned Lists.
Merge pull request #207 from L-Henke/multiSubKey

Implemented multi sub-key support
Merge pull request #213 from aBothe/pr3

Handle possible NullRef/JsonSyntaxException in Drop.deserialize()