Feature/blocks

See merge request !5

For a variety of reasons, posgresql won't use the available actor,
type index to do an index only scan. We now just increase the user
note count, which will lead to slightly wrong counts in some cases,
but it's better than the potentially very slow count query.

This is purely a performance enhancement

External url if available, id if not.

Fix return type of /api/v1/follows

See merge request !3