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/_form.html.haml

@@ -7,7 +7,7 @@
       .text-muted
         = @role.description
 
-= semantic_form_for @role, url: admin_conference_role_path(@conference.short_title, @role.name) do |f|
+= semantic_form_for @role, url: @url do |f|
   .row
     .col-md-5
       = f.input :description