Enable the browser's spellcheck in tinymce

TNL-1621

common/lib/xmodule/xmodule/js/spec/html/edit_spec.coffee

@@ -38,6 +38,8 @@ describe 'HTMLEditingDescriptor', ->
 
       @descriptor.initInstanceCallback(visualEditorStub)
       expect(visualEditorStub.getContent()).toEqual('text /c4x/foo/bar/asset/image.jpg')
+    it 'Enables spellcheck', ->
+      expect($('.html-editor iframe')[0].contentDocument.body.spellcheck).toBe(true)
   describe 'Raw HTML Editor', ->
     beforeEach ->
       loadFixtures 'html-editor-raw.html'

common/lib/xmodule/xmodule/js/src/html/edit.coffee

@@ -105,7 +105,9 @@ class @HTMLEditingDescriptor
         setup: @setupTinyMCE,
         # Cannot get access to tinyMCE Editor instance (for focusing) until after it is rendered.
         # The tinyMCE callback passes in the editor as a parameter.
-        init_instance_callback: @initInstanceCallback
+        init_instance_callback: @initInstanceCallback,
+
+        browser_spellcheck: true
       })
       tinymce.addI18n('en', {
         ###