Add start and completion count to volumetrics model
Change volumetrics graph to show total completion
Remove unused code
Merge branch 'master' into change_mean_calculation

Conflicts:
	app/assets/javascripts/fco/views/volumetrics-completion-number.js
Merge pull request #137 from alphagov/change_mean_calculation

Replace mean completion rate with total completion rate on the FCO volumetrics graph