Tinymce codemirror

This is a tinymce plugin to seamlessly use the already existing code mirror package in umbraco as the source editor.
The tinymceconfig.config is updated to seamlessly replace the code plugin with the new codemirror plugin. (And the user can switch back to code here if they need to for some reason.)

Other features:
-  Cursor location in text is maintained when switching back and forth.
-  Macro contents are suppressed on opening the source editor.  This should be done as it make it easier to review and edit, but also because it prevents editors that don't understand how a macro works from making changes to the macro text then saving only to have them lost.  Now a placeholder is just displayed in the source code so that cant happen.  The macro preview will render again when the page is saved.


This is a version of https://github.com/umbraco/Umbraco-CMS/pull/107 for Umbraco 7.
Feature request here: http://issues.umbraco.org/issue/U4-2604

![screen shot 2014-09-05 at 3 33 54 pm](https://cloud.githubusercontent.com/assets/458367/4170545/b14af862-3533-11e4-9776-330e75f3a52a.png)