Refactoring #1258

Updated by pospelov over 4 years ago

It looks like that all methods involved into copying of ParameterizedItem through XML machinery, namely
writePropertyItem, writeProperty, writeItemAndChildItems, readProperty, etc

can be moved outside of the class, in some static class presumably. Advantages will be
* SessionModel is not so terribly huge anymore
* Actions, –§ctions, like copying parameterizedItem can be done outside of SessionModel context