added tracking for when students encounter intervention points (currently stored in db)
moves other relevant code to new analytics module
adds page to download intervention point deployments data
adds error check to csv file creation
Merge pull request #60 from penzance/feature/user_tracking

feature/user_tracking
Merge branch 'master' into feature/additional_tests

Conflicts:
	ab_tool/exceptions.py
	ab_tool/templates/ab_tool/control_panel.html
	ab_tool/urls.py
	ab_tool/views/main_pages.py
merge with master resolved; edits to models; download data changes propogated