extends video element

Here we go.
Thanks for the input, looks way cleaner now.
I decided to leave the cast icon out and make the icon part of the controls.
WDYT?
Best regards,
Thorsten
Consider using declarative on-* handlers instead of doing things imperatively in the element.

You can put it directly in the definition: `<polymer-element .. on-seek="{{onSeeked}}">`