Excessive database privileges

[Changaco]

In #1311 I've finally added a protection against the deletion of the entire production database by mistake, however it's still possible to drop or truncate an entire table, especially a "leaf" table like repositories that isn't a dependency of any other object. Ideally the webapp should only be able to do what it's supposed to (SELECT, INSERT, UPDATE, DELETE), and DB admins should also be restricted to that same subset of commands by default, so that dropping a table would require executing SET ROLE dangerous first.

Relevant article: Auditing Users and Roles in PostgreSQL.