Add DownloadMagickImages and some fix

[kurema]

To keep compatibility, I added new methods for MagickImageCollection instead of replacing.

This PR includes other small fixes.

• Use ToLowerInvariant() instead of ToLower().
  • ToLower() returns weird value in some culture. Ex. In "tr-TR", "I".ToLower() returns ı.
  • Microsoft Docs says Use the String.ToUpperInvariant method instead of the String.ToLowerInvariant method when you normalize strings for comparison here. So maybe I should've used ToUpperInvariant() instead.
• Support for URL like icon.png?size=32.
• Add try{}catch{}. I encountered too many Exceptions.

They are not tested enough and some methods have been added in my sense. Please test and modify it to match the project policy.