Add "Test" functionality to Event Sources

I have found the new "Test" button on the Datasources' LogicModule setup pages to be invaluable for testing which hosts are associated with my "Applies to" filter. I can make a change to the filter and then get instant feedback, pointing out typographical errors, mispellings, or even possibly that I got it correct!

This will be equally valuable for the Eventsources LogicModule setup pages.