Audit changes to User and Client models

[reginafcompton]

We want to better track who-is-doing-what to the Authserver (via Facet). To this end, the data models need a couple new fields.

At the very least, I suggest adding the following fields to the User and Client. These fields will point to a User id:

• created_by
• updated_by

I can see an argument, however, for adding more discrete annotations, like, deactivated_by for the User, or secret_deleted_by in the Client model.

@vykster - what do you think? can you flesh out these requirements for @gregmundy?

[reginafcompton]

Relates to https://github.com/brighthive/facet/issues/93