Implement track requests and add the track organizer role

About track requests:
Create migration that adds the fields submitter_id, state, and
cfp_active to Tracks
Add validations and the self_organized? method to the Track model
Create a new TracksController outide of the admin namespace
Create the relevant views for index, show, new and edit
Modify the admin views for tracks to include extra info for
self-organized tracks

About track organizers:
Create the role when a self-organized track is created
Define track organizer abilities
Modify the roles views and controller to handle the new role

The route for Roles#edit needs to have higher priority than the nested
routes for track roles, otherwise, the word edit in the url is matched
as a track with short_name edit

app/views/admin/roles/_users.html.haml

@@ -14,7 +14,7 @@
           - if ( can? :toggle_user, @role )
             %td.text-right
               = hidden_field_tag "role[user_ids][]", nil
-              = check_box_tag @conference.short_title, @role.id, (@role.user_ids.include? user.id), method: :post, url: "/admin/conferences/#{@conference.short_title}/roles/#{@role.name}/toggle_user?user[email]=#{user.email}&user[state]=", class: 'switch-checkbox', data: { size: 'small', off_color: 'warning', on_text: 'Yes', off_text: 'No' }
+              = check_box_tag @conference.short_title, @role.id, (@role.user_ids.include? user.id), method: :post, url: "#{@url}?user[email]=#{user.email}&user[state]=", class: 'switch-checkbox', data: { size: 'small', off_color: 'warning', on_text: 'Yes', off_text: 'No' }
           %td= user.id
           %td= user.name
           %td= user.email