Scrawl-canvas v8 - Canvas test 019a

Gradient and Color factories - transparency - alternative approach using Cells instead of images

Test purpose

Use the four canvases to display a separate image, defined in the DOM.
Check that the `scrawl.createImageFromEntity` functionality works, and that we can capture and use blurred images created dynamically from the originals.
Create four (radial) gradients, each with a transparent hole in the middle. We are testing the following values for CSS transparency:

"transparent"
"rgba(0,0,0,0)"
"#00000000"
"#0000"

Check that all canvases display as expected, with in-focus areas of the image centred either on the mouse cursor, or in the middle of the canvas.

Touch test: should work as expected