Enforce project schema from the Entity Service

[nbgl]

I propose that the clkhash CLI download the hashing schema from the Entity Service, as a way of ensuring that the hashes conform to the project schema. This is a way of forcing all parties to use the same schema.

Related to n1analytics/entity-service#207 (private repository), which is a proposal to add a way to download the hashing schema from the Entity Service.

Aha! Link: https://csiro.aha.io/features/ANONLINK-31