[FIX] mass_mailing: ensure mailing snippets are in same window as others

Mass Mailing needs to extend the registry of wysiwyg snippets but
couldn't do so because they didn't live in the same window. This moves
the mass mailing snippets to the top window.

addons/mass_mailing/static/src/js/mass_mailing_widget.js

@@ -14,6 +14,7 @@ var MassMailingFieldHtml = FieldHtml.extend({
     xmlDependencies: (FieldHtml.prototype.xmlDependencies || []).concat(["/mass_mailing/static/src/xml/mass_mailing.xml"]),
     jsLibs: [
         '/mass_mailing/static/src/js/mass_mailing_link_dialog_fix.js',
+        '/mass_mailing/static/src/js/mass_mailing_snippets.js',
     ],
 
     custom_events: _.extend({}, FieldHtml.prototype.custom_events, {
@@ -33,9 +34,7 @@ var MassMailingFieldHtml = FieldHtml.extend({
         // All the code related to this __extraAssetsForIframe variable is an
         // ugly hack to restore mass mailing options in stable versions. The
         // whole logic has to be refactored as soon as possible...
-        this.__extraAssetsForIframe = [{
-            jsLibs: ['/mass_mailing/static/src/js/mass_mailing_snippets.js'],
-        }];
+        this.__extraAssetsForIframe = [{jsLibs: []}];
     },
 
     //--------------------------------------------------------------------------