Implement track/index action for API

app/controllers/api/tracks_controller.rb

@@ -0,0 +1,5 @@
+class Api::TracksController < Api::ApplicationController
+  def index
+    @tracks = Track.all
+  end
+end

app/views/api/tracks/index.rabl

@@ -0,0 +1,6 @@
+collection @tracks
+
+attribute :id
+attribute :name
+
+node(:sound_url, :if => ->(t) { t.sound? }) { |t| api_sound_url t.sound }