Responsive image gallery block

[pyronaur]

Issue Overview

Galleries alignment is off on mobile devices:

Caused by:

	margin: 0 16px 16px 0;

at .wp-block-gallery.aligncenter .blocks-gallery-image, .wp-block-gallery.alignleft .blocks-gallery-image, .wp-block-gallery.alignright .blocks-gallery-image, .wp-block-gallery .blocks-gallery-image

Possible Solution

Maybe use CSS Grid instead of Flexbox? People with CSS grid will get a column of images, which isn't all that bad. By using grid margin could be replaced with grid-gap - this seems like the exact thing the grid spec was designed for.

If CSS Grid isn't an option - that margin needs to be cleared up so that the gallery causing an unsymmetrical 16px gap on the right.

[karmatosed]

CSS Grid is planned to be used @justnorris, so a great idea to bring it in for this.

[jasmussen]

I'll take this one.

[jasmussen]

This issue is fixed by #5217.