Update to work with grails 2.4.2

Burt, these are the changes that I discussed with you at GR8Conf US. Unfortunately the build fails because of the test-app step, and there don't seem to be any tests, so I'm not sure if that is expected, or if I'm running the incorrect commands (i.e. "ant"), let me know if you'd like me to try something different. Thanks!

Removed references to PluginManagerHolder (removed in Grails 2.4), and
replaced with Holders.getPluginManager()

Updated the jquery plugin from 1.8.2 to 1.11.0.2, as recommended here:
http://grails.org/doc/2.4.2/guide/upgradingFrom23.html