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

.rubocop.yml

@@ -30,3 +30,4 @@ Metrics/BlockLength:
   Exclude:
     - 'spec/models/conference_spec.rb'
     - 'spec/features/ability_spec.rb'
+    - 'spec/models/ability_spec.rb'