Uses `module()` instead of `discourseModule()`, native getters instead of `.get()`, fixes some assertions, uses the store instead of creating models directly
There are two possible ordering for categories shown in sidebar with
this commit.
When the `fixed_category_positions` site setting is enabled, the
categories are ordered based on `Category#position` which is a configurable
option by the user. When said site setting is disabled, the categories
are ordered based on `Category#name`.
The categories in Sidebar are also sorted in such a way where child
categories are always ordered right after their parents. When multiple
child categories are present, the child categories are ordered based on
the ordering described above.
Using arrow functions changes `this` context, which is undesired in tests, e.g. it makes it impossible to setup things like pretender (`this.server`) in `beforeEach` hooks.
Ember guides always use classic functions in examples (e.g. https://guides.emberjs.com/release/testing/test-types/), and that's what it uses in its own test suite, as do various addons and ember apps.
It was also already used in Discourse where `this` was required. Moving forward, it will be needed in more places as we migrate toward ember-cli.
(I might later add a custom rule to eslint-discourse-ember to enforce this)
We used many global functions to handle tests when they should be
imported like other libraries in our application. This also gets us
closer to the way Ember CLI prefers our tests to be laid out.
This is where they should be as far as ember is concerned. Note this is
a huge commit and we should be really careful everything continues to
work properly.
