lots of changes, all about video playing: don't rely on prefinishmark, it didn't work; re-rewritten the video widget from scratch, it uses info from snc to convert to video time, and then it uses the videos. It still relies on functions within ktlx package, which doesn't make it flexible, but it's really hard to use a **clean** way to work around it
video should work fine, tested on example dataset (bob), there are still some bugs in the implementation
use partial instead of lambda: lambda reuses the same argument while partial behaves as expected
raise exception when the video is not found and change label of pushbutton (not really informative, but it's straightforward)'