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/tracks/_form.html.haml

@@ -13,4 +13,6 @@
       = f.input :short_name, hint: "A short and unique handle for the track, using only letters, numbers, underscores, and dashes. This will be used to identify the track in URLs etc. Example: 'my_awesome_track'", input_html: { required: 'required', pattern: '[a-zA-Z0-9_-]+', title: 'Only letters, numbers, underscores, and dashes.' }
       = f.input :color, input_html: {size: 6, type: 'color'}, required: true
       = f.input :description, input_html: {rows: 2, data: { provide: 'markdown-editable' } }, hint: markdown_hint
+      - if @track.self_organized?
+        = f.input :cfp_active, label: 'Allow event submitters to select this track for their proposal'
       = f.action :submit, as: :button, button_html: { class: 'btn btn-primary' }