Enable the simple mode addon for CodeMirror

[Belgabor]

The simple mode addon allows extension authors to write new CodeMirror modes in a more simple (regex-based) manner.

Reference: http://codemirror.net/demo/simplemode.html

The issue was briefly discussed on the google group: https://groups.google.com/forum/#!topic/brackets-dev/hoL6w3Iwg-M

[sprintr]

@marcelgerber We can close this one as well.

[marcelgerber]

This will be possible in Release 1.4
Closing.