Removed separate Code/Value models in favor of single model
Remove last migration
Remodel EA Codes and values
Changed society back to FK from EAVariableCodedValue
Updated load/clear for EA Societies
Add indexes on EAVariableCodedValue
APIs and serializers for remodeled EA

Also fixes to FilterSet bugs.
Add support for ea_variable_codes in find_societies

With a list of EAVariableCodeDescription IDs, find_societies now
returns the societies coded with that value.
API clients for EAVariable and EACodeDescription
Update angular search to show/search EA Vars

Refactored search controller somewhat
Merge pull request #9 from NESCent/remodel_ea

Refactor EA variable value model, prototype UI