remove global dojo references from dijit

[bill]

Menu.js and RichText?.js have lingering references to the dojo global. Presumably this will break multi-version dojo support in some obscure cases:

• Menu inside of an iframe (clicking the iframe opens the menu)
• removing stylesheets from an editor

[bill]

In [26973]:

Fix reference to dojo global in Menu, refs #14228 !strict.

[bill]

In [26974]:

Fix reference to dojo global in Editor, and add automated tests for Editor's addStylesheet()/removeStylesheet() methods, fixes #14228 !strict.