Change videos names from `avi` to `mp4`
Return empty array if empty event files

instead of failing with an error message
Display `N/A` when no events detected
Merge branch 'master' into feature/evaluation
Merge branch 'master' into feature/evaluation
Merge branch 'master' into feature/evaluation
Merge pull request #3 from StreakyCobra/feature/evaluation

Feature/evaluation
If a second arg is given to markus, assume it is a video file
Use WebKit to display editor
Merge branch 'master' into dev_lwk3