Refactor gem to utilize the Edoxen gem

[ronaldtse]

Currently the bipm-data-importer implements an object model for BIPM outcomes. The BIPM outcomes are actually based on the Metanorma resolutions model, which is now renamed to "Edoxen".

Once the new Edoxen gem is implemented, we can refactor the bipm-data-importer to use / extend from Edoxen directly. This allows us to better manage resolutions and outcomes from different bodies.

Depends on:

• Implement the Edoxen gem edoxen#1