Add an optional :sha1password authentication strategy.

This allows for an easy import of data from FluxBB, which uses
SHA1 for hashing its password. Users can keep their passwords
this way; newly registering  users will always use BCrypt, though.
Forums may be empty; don't crash then.
Unique forum names are not required.
Add a FluxBB import tool.

This works! O_o
Also download avatars in FluxBB import script
Add 'Mark all as read' button