Small style tweak proposal on /samples page

[chrisk-7777]

Regarding: https://excaliburjs.com/samples/

The sample images might look more consistent if we apply a sensible aspect ratio to the image container. This does leave a letter box effect for some images, however, I think that is better than using cover, which would crop the images.

Optionally, in _data, we could provide a background color for the letterbox effect, but default to the Exalibur blue.

Current on left, proposed on right:

I have some other doc changes I'm working on for the Tiled Plugin page, happy to roll it into that if the above fits.

[chrisk-7777]

An example with the optional background attribute (a pink and green applied to exacalitris + jelly jumper):

[eonarheim]

I'm a fan! I support these proposed changes!