[Feature] Need better color theme

I've just quickly put together the color theme, it is really bad and not very readable.

The default theme is stored in this file: https://gitlab.com/bztsrc/meg4/-/blob/main/src/misc/theme.gpl

Restrictions: has to be light foreground on a dark background, preferably on a grayish background close to #444444 (which is the official background color on the MEG-4 Floppy Drive screen). Otherwise foreground colors, menu background, selection background etc. totally up to you.

Cheers, bzt