NHT: Link to an individual stat

### Rationale
For highlights (in emails), as well as future features (e.g. allowing admins to approve user-suggested stats), as well as encouraging users to share and create their own stats... we'd like to be able to link to a specific stat.

### Implementation/design questions
@justinbmeyer do these requirements sound okay to you?
- Linking to a stat will seek the video to the right spot
- Video will loop for easy rewatching
- Video will not autoplay

### Relevant YouTube API docs
YouTube supports [start](https://developers.google.com/youtube/player_parameters#start), [end](https://developers.google.com/youtube/player_parameters#end), and [loop](https://developers.google.com/youtube/player_parameters#loop) parameters.