using max-width and max-height for package icons to avoid distortion and blurry upscaled icons, replace 50px by 48px

Conflicts:
	src/NuGetGallery/Content/Site.css
Merge pull request #1526 from NuGet/tomone/1525-PackageIconsDistortedAndBlurry

Fix 1525 Package Icons smaller than 50x50 look blurry on nuget.org