Remove old filenames.json files

They're no longer being used with the latest Datasource class
implementation.

Addresses https://github.com/openelections/core/issues/112
Use direct_links field from API

Use the direct_links field in the elections metadata API response
instead of the old direct_link field.

Addresses https://github.com/openelections/core/issues/114
Merge branch 'dev' into mo