Change way in which Wikimedia harvester	is called so that the path for saving files is specified on begin_wikimedia_harvest()
This is the function that actually requires a place to save files. Omitting it from the constructor allows us to make a
dummy WikimediaHarvester object for unit testing, without having to download and parse the enormous wikimedia dump.
Extensive extra unit tests for wikimedia harvester, tesing Flickr images, georeferencing, unicode filenames, and taxonomy parsing
Merge pull request #87 from hyanwong/wikimedia_unit_test_changes

Wikimedia unit test changes