32 (redo pull request) - use modals for videos

after reviewing 47 i realized i wanted to use text-center class instead of hard coded style.  Original pull request: 

Though i only handle a single url format for parsing the id, this story should be complete from the perspective of the videos page (use the url in the address bar from the youtube video, i.e. https://www.youtube.com/watch?v=caa0WrpxqyU )

you will need to run migrations as i added thumbnail to videos model. Old videos without thumbnails will need to be removed or backfilled with thumb urls.