Added Thumbs.db to gitignore

Please consider merging this.
David, Github is pointing out that there's no end-of-file end-of-line. I recall Matt explaining something about this to me at one point. He'd said something about Git requiring that all files have a trailing EOL at the end of the file in order to prevent merge complications.

Here's a link to an answer on StackOverflow about the same: http://stackoverflow.com/a/11414834.