Added object-fit and object-position to pc/npc images

Hi! I hope you don't mind unsolicited MRs. This is just a tiny fix I wanted to make for my group. I was going to do it with local custom CSS but then I figured I could submit it upstream.

What issues does this MR solve?

Currently the character images on the character sheet and the NPC sheet are hard-sized to a perfect square. This means that if your source image is rectangular, it gets distorted.

Source image:

Current appearance:

How does this MR address the issue?

I've added object-fit: cover and object-position: top to both instances of .actor-img in the stylesheet.

This means that the image as displayed in the sheets is 1. not distorted, and 2. consistent with the sidebar image in Foundry: