Pass DOM element, not jQuery object to XBlock initialisation.

The function initializeXBlock() expects a DOM element, and is passed one in most
cases.  However, when adding a new XBlock component in Studio, the function is
passed a jQuery object, which ends up being forwarded to the actual
initialisation function of the XBlock.

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

@@ -26,7 +26,7 @@ class @HTMLEditingDescriptor
     CUSTOM_FONTS + STANDARD_FONTS
 
   constructor: (element) ->
-    @element = element
+    @element = $(element)
     @base_asset_url = @element.find("#editor-tab").data('base-asset-url')
     @editor_choice = @element.find("#editor-tab").data('editor')
     if @base_asset_url == undefined

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

@@ -13,7 +13,7 @@ class @MarkdownEditingDescriptor extends XModule.Descriptor
   @explanationTemplate: "[explanation]\n#{gettext 'Short explanation'}\n[explanation]\n"
 
   constructor: (element) ->
-    @element = element
+    @element = $(element)
 
     if $(".markdown-box", @element).length != 0
       @markdown_editor = CodeMirror.fromTextArea($(".markdown-box", element)[0], {

common/lib/xmodule/xmodule/js/src/tabs/tabs-aggregator.coffee

@@ -2,7 +2,7 @@ class @TabsEditingDescriptor
   @isInactiveClass : "is-inactive"
 
   constructor: (element) ->
-    @element = element;
+    @element = $(element)
     ###
     Not tested on syncing of multiple editors of same type in tabs
     (Like many CodeMirrors).

common/static/js/xblock/core.js

@@ -69,7 +69,7 @@
         } else {
             block = {};
         }
-        block.element = element;
+        block.element = $element;
         block.name = $element.data('name');
         block.type = $element.data('block-type');
         $element.trigger('xblock-initialized');