data/lib: add pluralization helper

For future introspection/inflection.
data: import UK country level data

Because the UK dataset is large, we do a few new things in this commit.

    1) during import.py, we call countries.py simply to split the single
       giant UK CSV file into more manageable chunks, separated by transport
       mode, and written out into json.

    2) there is a LOT of bus data, so we import in chunks of 9999, simply
       to give the user some indication of progress on the console. This
       still takes forever...

It would be far superior to use mongodb's bulk operations, but that requires
mongodb >= 2.6 and pymongo >= 2.7, neither of which are available by default
in Ubuntu 14.04... sigh.