Lapis-chan v1.2.3 - File Extensions

I improved how file extensions are handled in the code so now cute_kitties.JPG will be detected properly. I changed how all extensions are read to use string.match instead of string.sub, and set the extension to lower case for detection purposes. This allows the code to be a bit cleaner, and even shorter in some places since I was able to merge webm and svg detection in the same if statements.