Groups page was loading fields that are only used on the group show
page, so move those fields to the GroupShowSerializer.
Also only fetch the default category and tag notifications once.
There are 5 visibility levels (similar to group visibility)
public (default)
logged-in users
members only
staff
owners
Admins & group owners always have visibility to group members.
* Introduced fab!, a helper that creates database state for a group
It's almost identical to let_it_be, except:
1. It creates a new object for each test by default,
2. You can disable it using PREFABRICATION=0
This change both speeds up specs (less strings to allocate) and helps catch
cases where methods in Discourse are mutating inputs.
Overall we will be migrating everything to use #frozen_string_literal: true
it will take a while, but this is the first and safest move in this direction
