`suspend` isn't a User attribute, but was being assigned to the frontend User model as if it was. The model has a computed property that depends on `suspended_till`, so instead of overriding this property, it's better to return relevant attributes.
Fixes a computed-property.override deprecation (https://emberjs.com/deprecations/v3.x#toc_computed-property-override)
* 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()
```
