Add script wicket user interface

The Community Script module does not currently have a Wicket User Interface. Adding a UI will make it much easier to add, update, and delete scripts.

Solves issue #GEOS-6483 (https://jira.codehaus.org/browse/GEOS-6483)
Not directly, because findScriptFile returns null if the File doesn't exist and I need the File even if it doesn't exist yet.  But, I can call through to findOrCreateFile.