Rewrite border drawing in `focus_node`
Rewrite border drawing in `focus_node`

6ad8160fadb24e422ebb75c7ea855ff2b4f2e402 introduced a blinking border
bug under the `mon == m` circumstances, the new code tries to keep it
simple while being exhaustive.

jbalint/bspwm,medisun/bspwm,XiKuuKy/bspwm,0re5ama/bspwm,JBouron/bspwm,netzverweigerer/bspwm,medisun/bspwm,baskerville/bspwm,netzverweigerer/bspwm,XiKuuKy/bspwm,nfnty/bspwm,JBouron/bspwm,JBouron/bspwm,ikn/bspwm,baskerville/bspwm,jbalint/bspwm,0re5ama/bspwm,nfnty/bspwm,0re5ama/bspwm,medisun/bspwm,ikn/bspwm,Stebalien/bspwm,jbalint/bspwm,Stebalien/bspwm,nfnty/bspwm