#42 Fix undo action and add new tests

Undo button now properly undoes the action

Add test for loading and saving models.
Add test for compiling abstract and concrete syntax models
Add test for checking deletion of element when undoing
Let testing framework Nightwatch handle the starting of the Selenium server for tests

Fixed Undo button now properly undoes the action Other Add test for loading and saving models. Add test for compiling abstract and concrete syntax models Add test for checking deletion of element when undoing Let testing framework Nightwatch handle the starting of the Selenium server for tests