Upgrade CodeMirror from 1.x to 4.1.

Geoserver is currently using CodeMirror 1.x.  Upgrading to 4.1 will make it much easier to support the community scripting module, provides better support for modern browsers, contains syntax highlighting for more languages, has a variety of themese, and several interesting plugins. 

Here a couple of related JIRA issues:

https://jira.codehaus.org/browse/GEOS-4815

https://jira.codehaus.org/browse/GEOS-5143

Thanks,
Jared