urls, models, control_panel.html, edit_track_weightings.html, track_pages
temp commit - media body
Can now save and update assignment method
removes track weight code for next pull request
better flow; removes unecessary model additions
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 branch 'feature/assignment_method' into develop

Conflicts:
	ab_tool/urls.py
Merge pull request #54 from penzance/feature/assignment_method

Feature/assignment method
Merge branch 'master' into feature/experiment

Conflicts:
	ab_tool/controllers.py
	ab_tool/exceptions.py
	ab_tool/models.py
	ab_tool/urls.py
	ab_tool/views/intervention_point_pages.py
	ab_tool/views/main_pages.py
	ab_tool/views/track_pages.py