Explicit datamodel support for external databases

We currently use key-uploaders to identify data from "external dbs". We also already have an external_id. We should add another repo datamodel quantity that identifies the external db that an entry comes from. This should be used to add a respective chart to the "user" tab in the search UI.

• add names for the other dbs
• change uploader to origin
• add the external_db metadata for the other dbs and reindex