Added scraper for historical maps from the Universiteitsbilbliotheek Utrecht

This scraper retrieves the dataset as described here:
http://www.opencultuurdata.nl/wiki/universiteitsbibliotheek-utrecht-kaarten/

An important obstacle I came across was the fact that an extra call to a different resource was needed to get the URL to the original image file. I solved this by adding an http request and XML parser to the `UUKaartenItem` class. This works, but might not be the most neat or correct way of dealing with such issues. I would like to here the opinion of others on this subject.

Because this commit is dependent on the previous commit, it also contains the commit from PR #35.