Add summary views for arguments

The text when creating arguments talks about a simple way for users to filter the text, but they actually can't do anything with it at all unless they happen to know how to configure a url that will take them to a filtered view or unless someone points them directly to it.

The current behavior for a view that uses arguments when no argument is provided is to not display anything. If we instead provide a summary view the end user will see a nice list of options and can click on one of them to get the filtered view. That seems more like the 'simple' result I would expect.

The fix is pretty easy and seems to work well. It even works with the CCK simpleviews field I am working on.