Implement track scheduling

Add track association to schedule
Show schedules in admin sidebar to track organizers
Allow track organizers to manage the schedules of their tracks
Don't allow self-organized track events to be dragged or unscheduled in
a conference schedule
Make scheduled events of self-organized tracks appear semitransparent in
conference schedules
Make the rooms of confirmed self_organized tracks appear semitransparent
and don't allow events to be scheduled to it in the conference schedules
during the dates of its track
Create admin/SchedulesController#new action
Add a button in admin/Schedules#index to create schedules for tracks
Add self_organized scope to Track
Modify Schedules#show to handle track schedules and show a unified
schedule
Allow track organizers to create new schedules for their tracks
Correctly identify scheduled and unscheduled events in Schedules#events
Fix Event#room and Event#time for when the event is scheduled in a track
schedule
Modify Program#selected_event_schedules to include the event_schedules
of selected track schedules
Modify Track#revoke_role_and_cleanup to destroy the track's schedules
and revert its events' state to new
Add tabs for conference and track schedules in admin/Schedules#index
Add button to Create/Show a tracks schedule in Tracks#index and #show
Fix concurrent_events in application_helper because of changes in
Program#selected_event_schedules
Do not take into account cfp_active in Event#valid_track
Modify EventsController#get_tracks accordingly
Enforce cfp_active of track to be enabled for proposals in
ProposalsController#create and #update
Add support for multiple schedules per track
Add selected_schedule_id to Track
Load EventSchedules of selected track schedules for conference schedules
in admin/SchedulesController#show
Modify SchedulesController#show to take into account only the selected
track schedules
Create Event#selected_schedule_id and use it in Event#scheduled? and
Event#time
Validate that an EventSchedule for an event of a self-organized track
belongs to one of the track's schedules
Add 'Manage' button in Tracks#index, #show that sends you to the admin
side of things
Add admin/TracksController#update_selected_schedule to update the
selected_schedule_id of tracks

app/views/admin/schedules/_day_tab.html.haml

@@ -5,7 +5,9 @@
 - date_event_schedules = @event_schedules.select{ |e| e.start_time.to_date.eql? date }
 .row
   - @rooms.each do |room|
-    .col-md-2.col-xs-6
+    - non_schedulable = room.tracks.self_organized.confirmed.any? do |track|
+      - !track.schedules.include?(@schedule) && (track.start_date..track.end_date).include?(date)
+    .col-md-2.col-xs-6{ class: ('non_schedulable' if non_schedulable) }
       .room-name
         - room_date_event_schedules = date_event_schedules.select{ |e| e.room == room }
         = room.name