Customizable Text Engine Support

[CryZe]

Currently we bring our own text engine that always turns the glyphs into paths. This isn't ideal when using a rendering backend that itself supports rendering text. In the browser it's much better to let the canvas render out the text as that results in fewer draw calls and also allows using any fonts other than our default fonts in the first place as the browser does not allow getting access to the font data of the fonts installed on the user's system. Additionally our current text engine does not support any font fallback, so using the underlying renderer's or even the system's default text engine provides much better font fallback support. So for all of these reasons and more it would be ideal to be able to swap out the text engine.

This actually is already mostly implemented.