Support Clements taxonomy table and international birding

add taxons model based on Clements data at
http://www.birds.cornell.edu/clementschecklist/Clements%20Checklist%206.
7.csv
use scientific names as foreign key linking sighting to taxon
add taxon_latin_name field to sightings
add taxons relationships to location, county, state, country
add taxons relationships to trips
add routing for taxons
add test fixtures for taxons and fix failing tests
assert that sightings have non-empty taxon_latin_name
add scaffolding for taxons, and some actual pages
add migrations for taxons table and foreign key in sightings table
Clements database migration cleanup

when creating a list of sightings, add taxon foreign key and species
foreign key (for now).
reintroduce zooming to google maps