* Use QUnit `module` instead of `discourseModule`
* Use QUnit `test` instead of `componentTest`
* Use angle-bracket syntax
* Remove jQuery usage
* Improve assertions (and actually fix some of them)
Note this commit also introduce a new {{d-popover}} component, example usage:
```hbs
{{#d-popover |state|}}
{{d-button label="foo.things" class="d-popover-trigger"}}
<div class="d-popover-content">
Some content
<div>
{{/d-popover}}
```
