Add query for visit visa applications

This should give us the number of unique visitors to a completion
page.

The regex should match:

    /customer/*/complete

But should NOT match:

    /customer/*/start/complete

So I've matched on characters, numbers and hyphens. I assume there
won't be anything else crazy in the URL. We'll see how that works.

https://www.pivotaltracker.com/story/show/71934810