don't show "return to them editor" inside editor

fixes: CNVS-21435

test plan
go to theme editor, 
make a change and hit preview
make sure the banner looks like http://cl.ly/image/2c3G0Z1R2k1J
and not: http://cl.ly/image/3w360M1g1P3l


Change-Id: I519ba1709320b959460cd28df99857771f74e98b
Reviewed-on: https://gerrit.instructure.com/57558
Tested-by: Jenkins
Reviewed-by: Colleen Palmer <colleen@instructure.com>
Product-Review: Colleen Palmer <colleen@instructure.com>
QA-Review: Ryan Shaw <ryan@instructure.com>

app/coffeescripts/bundles/theme_editor.coffee

@@ -3,6 +3,10 @@ require [
   'jsx/theme_editor/ThemeEditor'
 ], (React, ThemeEditor) ->
 
+  # framebust out so we don't ever get themeditor inside theme editor
+  if window.top.location isnt self.location
+    window.top.location = self.location.href
+
   React.render(React.createElement(ThemeEditor, {
     brandConfig: window.ENV.brandConfig,
     variableSchema: window.ENV.variableSchema

app/jsx/theme_editor/ThemeEditor.jsx

@@ -178,7 +178,7 @@ define([
                 </button>
               </div>
             </div>
-            <iframe src="/" style={{border: 'none', width: '100%', height: '100vh'}} />
+            <iframe src="/?editing_brand_config=1" style={{border: 'none', width: '100%', height: '100vh'}} />
           </div>
         </form>