Agreements do not follow I Agree specification

[motero2k]

Currently you can post an agreement without the required parameters by IAgree (Registry do not check this in a POST).

Two options:

• Make registry ask for all the required parameters:

Problem: The json models schemes do not work the same as the mongo schemes. In mongo we don't know if it is possible to use $ref without problems. If you put required in definitions.yourRefDefinition, mongo understand that definitions is required when it is not.

• Make I Agree less restrictive: At the time of this issue, this is the currently chosen alternative, at least for now.

Only check required at id,context,terms and type.