Add detection for HTML5 video autoplay

Furthering #353, this is a first attempt of adding a check. There are still some false positives, and the test suite is breaking in IE 10, but I wanted to get the concept in front of you guys to see if it was worth pursuing further.

The idea is include fairly small (1.4k mp4, 3k ogg) base64'd videos as the source src's, since the biggest issue was needing a video to test.