GeoIP lookups for issue #92
Round to the appropriate precision
Address Hanno's commentary

The cruel words from such an illustrious man have riven my heart.

Remove the inadvertent stub of a GeoIPTestCase class that was never meant to
be.  Actually call the teardown method for GeoIPIsolation.
Merge pull request #141 from rtilder/master

GeoIP lookups for issue #92
conform to arbitary hanno-style :)
Ryan won the snark battle - be consistent :)
Add / centralize degree <-> spatial resolution helpers.

ichnaea.models.DEGREE_DECIMAL_PLACES
ichnaea.models.DEGREE_SCALE_FACTOR
ichnaea.models.from_degrees
ichnaea.models.to_degrees
Add CellKey helpers to ichnaea.tasks, tidy up a bit.
Fix two typos in comments.
Note which keys are expected to be moving in testcase.
Add ichnaea.models.CellBlacklist.
Implement moving-cell blacklisting, close #134.