Should support SDF and bitmap fonts

[MSGhero]

By default, HaxeUI loads all fonts defined in XML as SDF. For a bitmap font, including the default Heaps font, this will render blocky shapes instead of the actual characters. There should be support for both types.

This is not noticeable using labels unless you actually set the font in a style, as TextDisplayImpl skips over font things and falls through to Heaps if the font name isn't defined.

This is a reminder for me to whip up a sample with both types in it.