Adjusted the autofill so that it should use the first page of the gallery as the cover.
Falls back to the old thumbnail if it breaks.

This actually matters now that we have namespaces, and there's no reason
not to bring it up to 255 characters. mysql is going to use 1 size byte
as long as we're below a maximum of 256 characters

Note that this password hashing change will cause an incompatibility
with a fraction of hashes made before this change. A migration is
necessary.