Video fullscreen icon fix

The video fullscreen icon was broken by a naming clash with the new gallery expand icon. Changed so they share icons.

The video player now relies on icons outside of the `images/video/` directory, but can't see this being an issue (and is better than duplicating icons)

SVGO isn’t that smart… unless maybe we can configure it to be smarter? It’d be nice if we could round points to two decimal places too.