Full node image is too large - reduce to 480px width

Issue Summary

The "large" image preset stretches to 640 px width. While this may be fine for some themes, it is definitely too big for many.
http://screencast.com/t/ZDgxZjBlZDct
Stretching it to the full width of the content area may be a good goal, but in doubt it should be rather smaller than wider.

So how about reducing it to 540x540 width. An image of the size 640x640 will not be the rule on most sites anyway, it is just too ginormous, and maybe an even smaller size, but somewhat more sqare like 480x480 might be more adequate.

So here is how it looks with 480px width and one sidebar:
http://screencast.com/t/ZGVhMWY0YzEt
And like this with 540, which should be enough for any big-image-lover:
http://screencast.com/t/MDY3ZDhkM2It

We had ugly Html image resizing, but this is just too bad #803934: Remove 300px width limit of images