user can rsvp from the event detail page feature

updated event detail page so that it doesn't break tests
Merge branch 'user-rsvp-event-detail-page' of https://github.com/treble37/bridge_troll into treble37-user-rsvp-event-detail-page
Students can RSVP from Index or Event Detail page

Students are asked their OS and 'Class Level'

Volunteers and Students are both now asked their 'Job Details'

This feature can be turned off with ENV['DISABLE_STUDENT_RSVP']
Show RSVP'd students on the event show page

Add some students to seeded event
Render session starts_at and ends_at in time zone always
Add simple_form to clean up radio button logic

Fix appearance of radio buttons on student RSVP when OS validation error occurs
Add gravatars to checkins tables
sign in via bootstrap modal dialog
Haphazardly sort past events on frontpage with datatables
/meetup_users is now /users, shows unassociated+associated users
add childcare info to organizer console
Event Show page sorts vols, greys out ones that did not attend an event
Merge branch 'master' of https://github.com/fionatay/bridge_troll into fionatay-master
user can now remove event sessions from new events
Set site-wide 'from' address

Config/initializers/devise.rb sets this for devise, but not for mailers.
https://www.pivotaltracker.com/story/show/41278297
Email volunteers when they volunteer

https://www.pivotaltracker.com/s/projects/608983
Merge branch 'master' of https://github.com/railsbridge/bridge_troll into rsvp-confirmation-mailer
Add db:test:prepare to script/bootstrap
Refactor user controller
Denormalize min/max session start/end times on event