Finalize the hostdb

Created by: VoidingWarranties

Move hostdb API endpoints from /renter/hosts to /hostdb

This PR is incomplete. The API documentation for the hostdb still needs to be updated to the new style. I'm waiting to update the documentation until I get comments about my concern below.

I was conflicted about whether to call the endpoint /hostdb or /hosts. /hostdb is more in line with naming endpoints after their modules (is it still the plan to make the hostdb its own module in the future?) but is potentially more confusing at first glance. Host DB might be confused as the database hosts use to store renter's files, instead of a database of hosts. /hosts make more intuitive sense, especially the full endpoint paths /hosts/active and /hosts/all) but is more easily mistaken for the /host endpoint.

I know this is nit-picky but since the API is being finalized I didn't want to skip over any considerations other people might have.