change preview layout to css-grid
change preview layout to css-grid

Use a CSS-grid for the preview images. This way, we have a fixed,
unified 25% width for every model.

codedust/gluon-firmware-wizard,freifunk-darmstadt/gluon-firmware-wizard,codedust/gluon-firmware-wizard,freifunk-darmstadt/gluon-firmware-wizard,codedust/gluon-firmware-wizard,freifunk-darmstadt/gluon-firmware-wizard