Changed way of propagating model change events:
* Now basic ModelRepo::change event must provide only plain object with changed fields, not model.
* Every collection of the model repo subscribes for the 'change' event of the repo.
* The handler smartly changes the collection's models if applicable (according to the field composition of the collection) and propagates another event for each actually changed model instance (e.g. model.1234.change).

Introduced Model::emitLocalCalcChange() method to be able to trigger change of any field's value of the model from any model instance (regardless of it's defined fields) without engaging backend.

ModelRepo improvements:
* introduced buildModel() factory-method
* made callModelAction to be able to call api with any HTTP-method