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.
* 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
* Split alias levels in mentionable and messageable levels.
* Fixed some tests.
* Set messageable level to everyone by default.
* By defaults, groups are not mentionable or messageable.
* Made staff groups messageable by the system.
