Active a canvas or graph

[BruceSherwood]

Currently when you create a canvas or graph nothing is displayed until and unless you create an object to be displayed in that canvas or graph, at which point the canvas or graph is "activated". There are situations where you would like to activate the canvas or graph immediately, to take up the next space on the page. In lib/glow/canvas.js and lit/glow/graph.js are the relevant activate functions.