desktop: Add flavours program to set colors

Switching from my custom, brittle, styling implementation `styler` to
the wonder `flavours` program which does exactly the same only with more
clarity, faster and - I would presume - more stable.

desktop/.config/mako/config

@@ -1,25 +1,18 @@
 sort=-time
 layer=overlay
-background-color=#2e3440
 width=300
 height=110
 border-size=2
-border-color=#88c0d0
 border-radius=15
 max-icon-size=64
 default-timeout=5000
 ignore-timeout=1
 font=monospace 14
 
-[urgency=low]
-border-color=#cccccc
 
-[urgency=normal]
-border-color=#d08770
 
 [urgency=critical]
 #on-notify=exec mpv /usr/share/sounds/freedesktop/stereo/message.oga
-border-color=#bf616a
 default-timeout=0
 
 [mode=do-not-disturb]