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/tracks/index.html.haml

@@ -0,0 +1,43 @@
+.container
+  .row
+    .col-md-12.page-header
+      %h1
+        Track requests for
+        %span.notranslate
+          = @conference.title
+
+  - if @tracks.any?
+    .row
+      .col-md-12
+        %table.table.table-hover#tracks
+          %thead
+            %th Name
+            %th Short name
+            %th Description
+            %th Color
+            %th State
+            %th Actions
+          %tbody
+            - @tracks.each do |track|
+              %tr
+                %td
+                  = link_to(conference_program_track_path(@conference.short_title, track.short_name)) do
+                    = track.name
+                %td
+                  = track.short_name
+                %td
+                  %p
+                    = truncate(track.description)
+                %td
+                  %span.label{style: "background-color: #{track.color}; color: #{ contrast_color(track.color) }"}
+                    = track.color
+                %td
+                  = track.state
+                %td
+                  = link_to 'Edit', edit_conference_program_track_path(@conference.short_title, track.short_name),
+                  method: :get, class: 'btn btn-primary'
+
+  .row
+    .col-md-12
+      - if can? :create, @track
+        = link_to "New Track request", new_conference_program_track_path(@conference.short_title), class: 'btn btn-success pull-right'