Ebird-checklists

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* Add date to Observation to simplify queries.
* Create separate Country model from Location.
* Create separate Region (state) model from Location.
* Create separate SubRegion (county) model from Location.
* Add Area model for defining groups of Locations.
* Mirror Country, Region, District and Area on Checklist and Observation
to speed up queries.
* Add Observation.identified for speeding up generating species lists.

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* Fix for eBird removing the project code from the observation data.

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* Update display and search fields in Django admin.

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* Update Observation admin to show checklist date, time, location and observer.

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* Reset the migrations.

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* Add ebird-codes for managing codes used by eBird.
* Removed PROTOCOL_TYPES from the Checklist model. ebird-codes provides it.