Make play()/pause() not throw for no/inactive timeline

As discussed:
http://lists.w3.org/Archives/Public/public-fx/2014OctDec/0009.html, item
1

This also makes "ready" a property of a player not its source content.

Generated from:

commit f3216b8a77ee51c7c2a73e7ecc37a6af4f49e5f3
Author: Brian Birtles <birtles@gmail.com>
Date:   Fri Oct 3 13:53:17 2014 +0900

    Make play()/pause() not throw for no/inactive timeline

    As discussed:
    http://lists.w3.org/Archives/Public/public-fx/2014OctDec/0009.html, item
    1

    This also makes "ready" a property of a player not its source content.