ISPN-3981 Enhance grouping API to support group manipulation methods

* First implementation. Added getGroup() and removeGroup() methods

This is the base implementation. Added methods to return and remove the keys from a group. This may be extended to support other functionality.

https://issues.jboss.org/browse/ISPN-3981
Also this has a nasty bug that if you had a removal and then a creation in that it would not return the key anyways, so it doesn't seem necessary to me.