Standardize how Problem and Video modules are loaded in the LMS and CMS preview pane

cms/static/coffee/src/models/module.coffee

@@ -4,16 +4,20 @@ class CMS.Models.Module extends Backbone.Model
     data: ''
 
   loadModule: (element) ->
+    moduleType = @get('type')
+
     try
-      @module = new window[@get('type')](element)
+      @module = if moduleType? then new window[moduleType](element) else null
     catch error
-      console.error "Unable to load #{@get('type')}: #{error.message}" if console
+      console.error "Unable to load #{moduleType}: #{error.message}" if console
 
   loadPreview: (element) ->
+    previewType = @get('previewType')
+
     try
-      @previewModule = new window[@get('previewType')](element)
+      @previewModule = if previewType? then new window[previewType](element) else null
     catch error
-      console.error "Unable to load #{@get('previewType')}: #{error.message}" if console
+      console.error "Unable to load #{previewType}: #{error.message}" if console
 
   editUrl: ->
     "/edit_item?#{$.param(id: @get('id'))}"

cms/static/coffee/src/views/module.coffee

@@ -4,8 +4,10 @@ class CMS.Views.Module extends Backbone.View
 
   edit: (event) =>
     event.preventDefault()
+    previewType = @$el.data('preview-type')
+    moduleType = @$el.data('type')
     CMS.replaceView new CMS.Views.ModuleEdit
         model: new CMS.Models.Module
             id: @$el.data('id')
-            type: @$el.data('type')
-            previewType: @$el.data('preview-type')
+            type: if moduleType == 'None' then null else moduleType
+            previewType: if previewType == 'None' then null else previewType

cms/static/coffee/src/views/module_edit.coffee

@@ -27,4 +27,10 @@ class CMS.Views.ModuleEdit extends Backbone.View
 
   editSubmodule: (event) ->
     event.preventDefault()
-    CMS.pushView(new CMS.Views.ModuleEdit(model: new CMS.Models.Module(id: $(event.target).data('id'), type: $(event.target).data('type'))))
+    previewType = $(event.target).data('preview-type')
+    moduleType = $(event.target).data('type')
+    CMS.pushView new CMS.Views.ModuleEdit
+        model: new CMS.Models.Module
+            id: $(event.target).data('id')
+            type: if moduleType == 'None' then null else moduleType
+            previewType: if previewType == 'None' then null else previewType