po/POTFILES.skip: add *.ui files

as per commit 815f8ee14f5c0906ef19a3c89adff43886fc924f, and to make
"make distcheck" happier
Bump 0.5.12
allow custom font scaling in panel_draw_label_text(), use in xkb

This fixes ID 3601007 - xkb plugin will always use custom color of font

https://sourceforge.net/tracker/?func=detail&atid=894869&aid=3601007&group_id=180858