Friendly urls for tracks

Don't use tracks ids in urls
Add short_name to tracks and use that in urls as the identifier

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20170603095900) do
+ActiveRecord::Schema.define(version: 20170629162450) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -485,6 +485,7 @@ ActiveRecord::Schema.define(version: 20170603095900) do
     t.datetime "created_at"
     t.datetime "updated_at"
     t.integer  "program_id"
+    t.string   "short_name",  null: false
   end
 
   create_table "users", force: :cascade do |t|