border-screen: Optional border around screen (#63)

Add option to specify border for screen / window in configuration file.

Can be useful when user turn off window decorations and need a subtle
hint or want strong window borders.
2 jobs for !7 with border_screen in 1 minute and 47 seconds (queued for 2 seconds)
latest detached
Status Job ID Name Coverage
  Build
passed #1750
build

00:00:48

 
  Distcheck
passed #1751
distcheck

00:00:59