Remove sliding effect on avatar mouseover

Might be controversial, thus the separate branch and PR.

This edit removes the "slide" that happens when you mouse over a person's avatar (including your own), leaving only the appearance of the nametag and the background shading. I tested with normal avatars, avatars with big wizard hats, mounted avatars, and mounted avatars with big hats; the worst that happens is that the uppermost part of the character's head (or part of the hat, if present) is obscured by the nametag if you're mounted.

I personally think this looks _way better_ than the weird juddering that happens at present, even with the caveat that a bit of forehead/hair/hat goes missing, but YMMV.