* 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()
```
Prior:
Entering `test after:5` and then removing the 5 via the search text field would result in the UI not updating
After:
UI updates after half a second
Removing it from the UI, removes it from the search field immediately.
Change the regex to detect filter words. This now matches what happens in search.rb, which gives a lot more flexibility (such as iterating over multiple `in:` terms)
Return [] when searchTerm is empty
Move .trim() to this.set('searchTerm', searchTerm) so it doesn't run twice (which was very obvious when watching the search term field)
More refactoring to make this a bit less complex
Update code based on review comments
FEATURE: Add common `in:` options
Tests for populating category and tags
Added acceptance tests for populating the Username and Category through the Advanced Search UI (will work on the other fields later)
Give the combo-box elements ids
Add acceptance tests for the rest of the advanced search UI (except for Tags, tags are evil)
