option to hide the file tree in exercises.

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: 20150903152727) do
+ActiveRecord::Schema.define(version: 20150922125415) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -79,6 +79,7 @@ ActiveRecord::Schema.define(version: 20150903152727) do
     t.string   "user_type"
     t.string   "token"
     t.integer  "team_id"
+    t.boolean  "hide_file_tree"
   end
 
   create_table "external_users", force: true do |t|