Added source code syntax highlighting plugin `codemirror`.

Added source code syntax highlighting plugin `codemirror` to CKEditor (using `codemirror_v1.06.zip`):

- http://ckeditor.com/addon/codemirror
- https://github.com/w8tcha/CKEditor-CodeMirror-Plugin

One would still want to check and manually correct the source code from time to time, because user friendly plugins for editing text never get it quite right or enable everything you want to accomplish.. Because watching and editing a not syntax-highlighted HTML source code is a thing of the past and [CodeMirror](http://codemirror.net/) seems to be a nice JS component for syntax coloring HTML and other languages that is also available as a plugin for CKEditor.