Configuring the inclusion of ~/.groovy/lib jars

In GRECLIPSE-592, we have created a way to configure the inclusion/exclusion of jars in ~/.groovy/lib on a per-project basis. There are 2 issues with it:

1. Should be able to configure the inclusion/exclusion workspace-wide.
2. There is a lag when the finish button is clicked since the groovy classpath container is updated no matter whether or not the option was changed. Either, there should be a "Refresh now" button that does the refreshing, or the refreshing should occur in the background as a WorkspaceRunnable (or both).