Rework drawing system to only draw what is necessary

[dsamarin]

Currently, all widgets are redrawn every time something needs to be updated. We should think about having each widget create it's own element. This might slow down re-sizing and allocation, however, but widgets will only have to draw to a single element and the browser will worry about superimposing each widget on top of each other. Events like onenter, onleave will be easier to implement this way.

[dsamarin]

Thanks to the magic of position: absolute, this has become a reality :) Work is beginning on suit.Window which is a rectangular space with its own element, coordinates, and canvas.