lml#347: Fix the continue button action.

- Add a hidden field to make sure the `save_and_lock` parameter
  expected by the controller is provided.
- Rename `AddUserSettings` => `CreateUserSettings`
- Remove `null => true` according to @Dantemss' comment.

app/views/student_exercises/_add_and_turn_in_free_responses.html.erb

@@ -77,11 +77,11 @@
     <center>
       <% confirm_message =  "After you turn in your answer, you can no longer change it. " +
                             "Are you sure you want to turn in your answer?" %>
+      <input type="hidden" name="save_and_lock" value="true">
 
       <div class="actions" style="padding-top:10px">
         <%= f.submit "Turn in my answer",
                 :data => {maybeConfirm: confirm_message, setting: 'skip_answer_lockin_message'},
-                :name => "save_and_lock",
                 :class => 'link_button maybe_confirm' %>
 
       </div>

db/migrate/20140613110759_add_user_settings.rb → db/migrate/20140613110759_create_user_settings.rb

@@ -1,11 +1,11 @@
 # Copyright 2011-2014 Rice University. Licensed under the Affero General Public
 # License version 3 or later.  See the COPYRIGHT file for details.
 
-class AddUserSettings < ActiveRecord::Migration
+class CreateUserSettings < ActiveRecord::Migration
   def change
     create_table(:user_settings) do |t|
       t.integer :user_id, :null => false
-      t.text    :settings, :null => true
+      t.text    :settings
       t.timestamps
     end