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.
* DEV: uses centrain eslint-config-discourse
Discourse project or plugins can now have a central configuration by doing:
`yarn add --dev eslint-config-discourse@latest`
* adds postinstall script
* renames `select-box-kit` into `select-kit`
* introduces `single-select` and `multi-select` as base components
* introduces {{search-advanced-category-chooser}} as a better component for selecting category in advanced search
* improves events handling in select-kit
* recreates color selection inputs using {{multi-select}} and a custom {{selected-color}} component
* replaces category-selector by a component using select-kit and based on multi-select
* improves positioning of wrapper
* removes the need for offscreen, and instead use `select-kit-header` as a base focus point for all select-kit based components
* introduces a formal plugin api for select-kit based components
* introduces a formal pattern for loading and updating select-kit based components:
```
computeValue()
computeContent()
mutateValue()
```
Robin Ward
Joffrey JAFFEUX
Mark VanLandingham
Régis Hanol
Maja Komel
Guo Xiang Tan
Rafael dos Santos Silva