Simplify play/pause handling (#410)

I found it awkward to listen to the video tags 'playing' and 'paused'
events, when we're controlling the state that defines what state it's
in in the first place.

This commit removes those listeners, in favor of just setting things to
the right state immediately when play(), pause(), or playPause() is
called.

Added play(), pause() methods for clarity.

renderer/views/player.js

@@ -78,8 +78,6 @@ function renderMedia (state) {
       ondblclick=${dispatcher('toggleFullScreen')}
       onloadedmetadata=${onLoadedMetadata}
       onended=${onEnded}
-      onplay=${dispatcher('mediaPlaying')}
-      onpause=${dispatcher('mediaPaused')}
       onstalling=${dispatcher('mediaStalled')}
       onerror=${dispatcher('mediaError')}
       ontimeupdate=${dispatcher('mediaTimeUpdate')}