Option to resize element to canvas size/ratio

[SoylentGraham]

Currently the canvas(and thus the content) is resized to fit the content rect.

There will be times where we want to make use of flexbox/uitoolkit's DOM alignment (leading, top, right align, match text etc), and I think the only real way to do that will be to set the .width and .height to the original canvas size.

The user can then scale, and align the rest of the dom appropriately.

• Check what image elements do (I think images are only ever backgrounds, so never dictate an element size??)