Added mappable and public_positional_accuracy fields to Observation; rake task to populate these fields; abilty to filter on mappable in Observations API
Bugfix: quality metrics weren't updating the observation when destroyed.
Fixed some mappable logic when adding quality metrics; Can now get observations from API where mappable is false
Merge pull request #346 from pleary/mappable

Added mappable and public_positional_accuracy fields to Observation; rak...
Switched people/stats to use site_id, ensured site gets set for new obs.
Merge branch 'master' of github.com:inaturalist/inaturalist

Conflicts:
	app/models/quality_metric.rb
Bugfix: places/edit was broken.
Removed long-running rake task from mappable migration.
Fixed bug with CSV generation that is causing some delayed jobs to fail; also some more preloading to speed up CSV generation, make it more efficient