added video embedding

Squashed commit of the following:

commit 96c1fc744c8f0fb5a2246c7230d0607f6f97a793
Author: Artem Suschev <Suschev.Artem@gmail.com>
Date:   Wed Oct 23 15:53:20 2013 +0400

    added video embedding
added stepic links support

Squashed commit of the following:

commit c483b13b61a542a01832e996fb7ad2b570d38ebc
Author: Artem Suschev <Suschev.Artem@gmail.com>
Date:   Wed Oct 23 17:12:53 2013 +0400

    added stepic links support