Feature request: Hot-refresh font files

[be5invis]

This will be super useful when you test fonts using this util.

Instead of using a standard font loader, the util will load the font files into memory (so the original file will not be locked and will allow overwriting) and render the preview images using the in-memory copy of the fonts.

An extra "refresh" button will be added into the UI. When you hit the button, all the "drawable"s will reload the font file into the memory and update the corresponded image.