Added a "Browse Animations" mode. It lets you browse the directories and animated gifs on the SD card.

I think with a little more work, this could replace the static list of animation modes (General, Christmas, Halloween, etc).  Since the directory names are limited to 8 characters, I added an index.txt file to each directory with a long name, and then read and display that instead of the folder name (seems like there should be a better way to support long file names...).