videoLinkShells: call video apis conditionally
timedMediaPlayerView: loopsElapsed -> elapsedLoops
timedMediaPlayerView: create elapsedLoops method

TimedMediaPlayerView::elapsedLoops is a get/setter for elapsed loops
timedMediaPlayerView: reset loop count on restart
videoLinkShell: bugfix: test seekOffset existence

should only not seek if seekOffset is undefined; if it is 0, seeking is
the correct action
videoLinkShell: bugfix: looped -> elapsedLoops

@jbenet when you change variables during a refactor, grep to make sure
nothing is still counting on the old variable name. you introduced this
bug when creating the TimedMediaInterfaceView and refactoring
VideoLinkShell to use it:
4d4d4e89a52f9d221ae67de7057dedc710f13c13
ad9738d99bc95cb06f1ba5fb63c7da96b61cd2f6