move to solid-auth-fetcher

the inrupt auth libraries no longer maintain sessions across page
reloads (inrupt/solid-client-authn-js#423)
which is better for strict security, but a dealbreaker for user
experience, so switch to solid-auth-fetcher for now.

the right solution here is to make swrlit auth library agnostic, which
will also involve putting together a cleaner typing system - the types
here are copied from solid-auth-fetcher which is super messy.