chanserv/access: Fix permissions checks in ROLE command.
chanserv/access: Don't allow changing +F via ROLE command.

Changing founder status via /cs role would require a fair amount of code
to ensure restrictions such as max_founders are obeyed. Simply do not
allow this.
chanserv/access: Apply more checks to foundership changes.

There should not be too many founders, hostmasks cannot be founders and
an entity can be a founder of a limited number of channels.