first steps in customizing fontset
transfer :fontset when using fixed-width/variable-width face mixins
don't specify base size for variable-width font in theme
move stuff from `ublt-appearance' to `ublt-font'
refactor `ublt-font'
fix theming messing up default font size
set up variable-width font only if `ublt-font' is loaded successfully
add font rescaling, configure fixed-width & variable-width fontsets
try to fix (unsuccessfully) various glitches with default font/fontset