Corrected config class structure

* removed bidirectional associations of config classes
* corrected config class structure in general
* changed ConfigSerializationTest to adapt the new class structure

Should fix #81 and closes #69.
Please check if I got it right.
Should be 1 to 0..* (?) because, every SyncedModuleSettings, must be linked to a SyncedSettings. (No part without the whole.)