The entire internals of the server now work using only NaiveDateTime,
since we know they are all UTC. At the fringes (LDAP, GraphQL, JWT
tokens) we convert back into UTC to make sure we have a clear API.
This allows us to be compatible with Postgres (which doesn't support
DateTime<UTC>, only NaiveDateTime).
This change is backwards compatible since in SQlite with
Sea-query/Sea-ORM, the UTC datetimes are stored without a timezone, as
simple strings. It's the same format as NaiveDateTime.
Fixes#87.
This is the smallest integer compatible with all of MySQL, Postgres and
SQlite.
This is a backwards-compatible change for SQlite since both are
represented as "integer", and all u8 values can be represented as i16.
