Includes:
- context menu for switching to sliders, only on variables.
- width, height, min, max properties consumed from VM.

Fixes #1853

It was 435KB. Now it's 5KB. I used SVGOMG: https://jakearchibald.github.io/svgomg/

Root cause is probably the flex implementation on Safari.

Update calls to addSprite2 to use new API for adding sprites. Cleanup sprite3 representation for uploading a new sprite from an image.

Fixes #1955

Also extract the "supportedBrowser" logic into a helper (rule of 3)