Volunteers, positions and days and volunteers list for admin, volunteering option for attendees
Merge branch 'final_volunteers' of https://github.com/differentreality/osem into differentreality-final_volunteers

Conflicts:
	app/models/conference.rb
	app/models/registration.rb
	app/views/admin/conference/_sidebar.html.haml
	app/views/conference_registration/register.html.haml