Create standalone video, sound, & image testers

[toomanybrians]

Lots of people have questions and issues figuring out if the have the right codecs to play a certain video or sound file or to view a certain image.

We should create a standalone test tool that can be run like:

mpf asset_test myvid.mov

It could also pop up the metadata it can discover about the asset, including duration, resolution, etc. and maybe have a basic media player (play/pause/jump) for videos and sounds.

It could also have forward and back buttons to test other files in the current folder.

This would be pretty quick and easy to build.