Login & Alert Styling

Styled login form to match planner and admin interfaces.
Global styling and view for alerts/notices/errors.
Export planner state as CSV

Created a PlannerHelper module
— Export state of planner as CSV and associated paths/routes through
download controller
— new method called clear_enrolment_planner_session

Created GET route for enrolment_planner
— modified planner controller to perform no task on GET