Refactoring of Domain structure code

* Added const access to some Unit descriptor attributes

(references #165)
Refactoring of Domain Class InputData code

(references #165)
Fix of bugs with input data in AdvancedDomain descriptor

* Fixed wrong internal storage of input data value
* Fixed wrong input data list update when deleting a Unit
* Fixed forgetting to remove an InputDataDescriptor if became empty
Refactoring of Domain Class Events code

(references #165)