Basic text support for CocoonJS

Because there isn't a CSS context when running in CocoonJS' accelerated mode, an additional function, determineFontHeightInPixels, is needed to calculate the total height of 'gM' using a method of drawing it to a canvas and counting total pixel height.

Then, because the line-height CSS value doesn't exist either, an approximation value of 1.2 is used to match its most commonly set "normal" value across fonts.