Add support for more than three screens.
Add support for more than three screens.

The change relates to the commands "focus-screen" and "throw-screen". It allows that more than three screens can be configured.

Uses new "screens" variable in the configuration to define the number of screens.

hooplaaa/Amethyst,ianyh/Amethyst,hooplaaa/Amethyst,egabancho/Amethyst,cevaris/Amethyst,egabancho/Amethyst,olsonpm/Amethyst,m4rw3r/Amethyst,m4rw3r/Amethyst,ianyh/Amethyst,ianyh/Amethyst,olsonpm/Amethyst,cevaris/Amethyst,ianyh/Amethyst,ianyh/Amethyst