This pr replaces `{{{ }}}` usage by a {{html-safe}} helper. While it doesn't solve the underlying issue, it gives us a path forward without risking breaking too much existing behavior.
Also introduces an htmlSafe computed macro:
```
import { htmlSafe } from "discourse/lib/computed";
htmlDescription: htmlSafe("description")
```
Overtime {{html-safe}} usage should be removed and moved to components properties or specialized components/helpers.
This allows you to temporarily disable components without having to remove them from a theme.
This feature is very handy when doing quick fix engineering.
* fill blank space when no theme is selected
* animate row's height in themes/components list when selecting, and hide children list
* show warning when you move to a different page and have unsaved changes
* refactor `adminCustomizeThemes.show` controller
* allow collapsing/expanding children lists
* fix a bug when adding components to a theme (changed the way it works slightly)
* a bunch of other minor things
romanrizzi
Joffrey JAFFEUX
Osama Sayegh
Penar Musaraj