lupan-wm: M-S-F6 switchs theme, use st as terminal

st-lupan-0.8.5.diff adapted from
http://st.suckless.org/patches/solarized/st-solarized-both-0.8.4.diff by
- change to windi colors
- switch colors with F6 or select with SIGUS1/SIGUSR2
- use font Iosevka Slab Light

xsession/.xsession

@@ -23,7 +23,7 @@ emacsclient --eval nil -a '' &
 xsettingsd &
 
 if which lupan-wm > /dev/null; then
-    xsetroot -solid '#0ea5e9'
+    xsetroot -solid '#4a4a4a'
     lupan-clock &
     xsetroot -cursor_name left_ptr
     exec lupan-wm -s 20