mapable? updates

This change updates the mapable? method in family by converting the
values to floats rather than integers.  The reasoning here is that
a longitude of -0.967373 (for example), converted to an integer,
evaluates to 0.0, which fails the mapable? check.  We also update
mapable? in the group model to match that in family.

Note that a lat/long of 0.0 are actually valid, however this location
does not fall on land and therefore can probably be considered invalid.
Merge pull request #276 from mattt416/update_mapable

mapable? updates