Add util scripts to update test data files

[alastair]

We have lots of data files in https://github.com/alastair/python-musicbrainzngs/tree/master/test/data which were downloaded manually from the webservice. Some new features of the ws are not included in these files, and they should be updated in order to improve functionality/tests.

I was thinking of creating a type of config file that contains entity/id/includes and a download script that can be re-run from time to time to re-query the ws and save the results in the data files.