Removes ApplicationHolder, scopes assets to work better with asset-pipeline

This Removes references to ApplicationHolder as it no longer exists in Grails 2.4. Currently it uses grails.util.Holders which is still not the best recommendation. It is probably preferable to Create a plugin specific holder that has the bean registered.

Also we nest the font-awesome resources so they do not clash with twitter-bootstrap plugin (The same will need to be done for that plugin).

Also updated the plugin version to 2.3.6