Block in editor with media selected.
- Adds STL as a media type for uploads.
- Adds STL as a filter in media browser for picking items.
- Provides editor block for embedding a viewer, based on viewstl plugin.
- Editor block uses media browser to pick model.
- Options to set model color, background color, border, auto rotation, etc.
- Editor block updates with changes to match what live site would display.
- Relevant elements are prefixed to allow displaying multiple viewers on one site page.