Remove unused JS code from map
Slight map refactor, aiming to use JS from map for front page 'where' search
Add some more to the front page
Add an api for listing all the values of a field, and the number
of records they appear in.

Available at /api/values/<field_name>
Returns results in the form:
{
	"field": <field_name>,
	"results": [
		"num": <num_matching>,
		"val": <field_value>
	], ...
}
Use select2 and the new field values api to populate the period
and building type advanced search fields.
Hook up the new select2 fields to filter our results