Ports changes to models and model tests along with some settings changes from feature/tracks_activation
changes to canvas interaction layer to better reflect the skd's use of exceptions
adds dowload data functionality
cleans up and adds tests to selection pages
makes tests more unit and less integration
changes url to a URLField
adds many-to-many stage url relation
Merge branch 'feature/new_models' into develop
Merge branch 'feature/canvas_api_changes' into develop
Merge branch 'feature/main_pages_changes' into develop
Merge branch 'feature/selection_pages_improvements' into develop