implement own width/height, read values from dom
implement own width/height, read values from dom

according to https://github.com/videojs/video.js/issues/2282 videojs' width() and height() aren't supposed to return the 'real' width and height, instead returning the values the player was initialized with.
This fix reads the current player's dimensions from DOM and makes the ad-plugin use these instead.

shawnbuso/videojs-ima,valse/videojs-ima,goskipstone/videojs-ima,fem-inc/videojs-ima,tv2/videojs-ima,ypavlotsky/videojs-ima,ypavlotsky/videojs-ima,googleads/videojs-ima,fem-inc/videojs-ima,shawnbuso/videojs-ima,tv2/videojs-ima,tape-tv/videojs-ima,valse/videojs-ima,tape-tv/videojs-ima,googleads/videojs-ima,goskipstone/videojs-ima