Implement missing & remaining pieces propagation + cleaner forms

spec/models/offline_spec.rb

@@ -9,6 +9,7 @@
 #  name             :string           not null
 #  remaining_pieces :integer
 #  start_time       :datetime         not null
+#  submitted        :boolean
 #  created_at       :datetime         not null
 #  updated_at       :datetime         not null
 #  contest_id       :integer          not null