first pass: html and backend changes for track weights
temp commit: changes to control panel and related backend; new edit_track_weights HTML
updates to edit_track_weights HTML; deploy_intervention_point updated to deploy depending on assignment_mode; exceptions added; backend validation added;
moves non-page methods to controllers.py
Adds modal warning admin user if missing track weights
adds course_id to db filtering
.gitnore update to ignore env/
Adds check for assignment_mode weighted_random to finalize
removes print statements
Merge pull request #55 from penzance/feature/track_weights

Feature/track weights
Merge pull request #54 from penzance/feature/assignment_method

Feature/assignment method