Adding UrlUtils

I've added a class called `UrlUtils` which is meant to perform the common operations when building a URL in Groovy. This includes appending a queryString (and including a '?' or '&' character as required) and ensuring a URL ends with a trailing slash.

There were a few duplicate implementations of this scattered through our code, and they were tested independently.

Please don't review whitespace as some of these files are pretty mixed-up with tabs and spaces. I will do a tidy-up when this (and other branched) work is back on master.