Register bot user

[titpetric]

We have a special user type for bots already defined. We need applicable user creation APIs that will allow a registered user to create a bot account, and retrieve it's login credentials in order for a bot to interact with our full API.

We already have /users/create that may create our bot users, but we need something to link the originating account (i.e. "Tit Petric" created bot account "Servant" - we need a relationship in the database which will let the principal account list the bot accounts he created, as well as any credentials that we need to use the bot account).

• link bot accounts to main user account that created them,
• enable listing bot credentials (public key + secret key),
• oauth2 client-credentials grant for bots to get a JWT token,
• ability to refresh JWT token based on previous JWT token,
• bots must not be able to log in with /auth/login

Related trello card here