bugfix: when elements are removed and added to the same list in a short time span and the change has to be executed in the JavaFX GUI thread, one event could overtake the other and the metamodel consistency checks would lead to elements not being added or removed
put traces in if-statements for performance improvements
Merge pull request #13 from mthiele/bugfix_list_operations_multithreading

bugfix: when elements are removed and added to the same list in a short ...