make a table for sightings, and fix broken add new species function
add update method to sighting
add destroy method to sighting
add region class
add region_id column to sightings table
add validation of presence of name for region class
region has many sightings association
add sighting belongs to region association
region has many species through sightings association
add species has many regions through sightings association
add index method to region controller
add new region
add create method to region controller
add update method to region controller
add destroy method to region controller
add dropdown menu for regions on sightings
make sighting index work for region
make sighting new work for region
create a way to view sightings from both species and region