7.0 No auto lines

Added tests and refactored some parts of the code. It's not possible to keep old lines as they are unlinked later by the base class. When the model is reloaded, it will try to load some line ids that are deleted.

Returning new lines as fresh id is a way to make it work correctly. The downside of this module is that when clicking on discard, it won't be able to refresh the model as the old lines were deleted. This problem is by design as lines should be added automatically and recreated automatically which means that they never wondered to save the state of the lines in case you want to discard changes.