[BostonGlobe] New. Nonstandard version of Brightcove.

[BostonGlobe] New. Nonstandard version of Brightcove.

Has a "data-brightcove-video-id" instead of a "data-video-id," otherwise
pretty much just Brightcove. Except the Globe isn't all Brightcove
videos, so fallback to Generic, too.

Also, abstract playlist_from_matches() from generic.py to common.py, and use
it here.

History of these changes can be found in
51170427d4b1143572a498dedaee61863a5b2c5b.