Twenty Ten, Eleven, Thirteen: add bottom margin to audio and video players.

Fixes #29146. Props mikeyarce, gregrickaby, DavidTheMachine, jeanyoungkim, ccprice.

Built from https://develop.svn.wordpress.org/trunk@30371


git-svn-id: http://core.svn.wordpress.org/trunk@30369 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fifteen: pinking shears.

Built from https://develop.svn.wordpress.org/trunk@30372


git-svn-id: http://core.svn.wordpress.org/trunk@30370 1a063a9b-81f0-0310-95a4-ce76da25c4cd