ZF2-28: no support to extra plugins like ordinary plugins


the class Zend_Dojo_Form_Element_Editor has ordinary plugins operations but doesn't allow us to use similar methods for extra ones.

extra plugins are part of {{dijit.editor}} component as can be seen here: http://dojotoolkit.org/reference-guide/dijit/…

suggested additions to class {{Zend_Dojo_Form_Element_Editor}} and suggested test units for being add to class {{Zend_Dojo_Form_Element_EditorTest}} can be found attached.

the fix for this depends on ZF-5711


Pull request to import this patch from ZF1 is sent: https://github.com/zendframework/zf2/pull/310

Pull request was merged by Matthew.