Separate font type and theme selection in settings

[maxRN]

Instead of choosing "light / sans" or "light / monospace" we should have two different categories, one for the theme and for the font type. That way users can change the font and theme indepently.

This also makes adding differents fonts or themes easier in the future.

[geekley]

This is now implemented, right? On 3.0.4 at least.

[geekley]

Though I'd like this option to be further improved, so I opened #142