Make seestar build with erlang R16B01

Erlang version 17 requires `dict:dict`,
but qualifying it this way breaks compilation
on older versions of erlang.

This change will likely break compilation with
version 17, but we're using R16B01, so stick
with that for now.
Add `registered` entry in .app.src for relx

Relx requires a `registered` value, so add in an empty one.