Fix Report a Problem functionality

The Report a Problem URL was being set incorrectly. This commit sets up a new `govukUrl` which will require production config.

I'm really pleased that this is now tested with Cucumber.

I don't think some of the things in `process_request` are correct, I'd like a second pair of eyes on them before I fix. Specifically:

    requestPath: req.path,
    requestUrl: setup.getFullUrl(req),