Consider a tweet embed a blocker
Merge pull request #17 from borkweb/5852-dont-push-tweet

Tweet embed should be considered a "blocker" when laying out widgets
Recalculate the blackout height when it is shifted down
Merge pull request #18 from borkweb/5848-subscribe-box-height

Recalc blackout height when injection is shifted down & don't create a gap when there isn't one