CLC-3726: Video thumbnail is read as "Group"

https://jira.ets.berkeley.edu/jira/browse/CLC-3726

CLC-3727: After video is "played" focus is on window and not on the video
https://jira.ets.berkeley.edu/jira/browse/CLC-3727

CLC-3728: Thumbnail should probably respond to both Enter and Spacebar keys to activate video playback
https://jira.ets.berkeley.edu/jira/browse/CLC-3728