Add server killing functionality

[jakestrahm]

The ability to close all current grip servers from within grip e.g. grip --killall

[anhtumai]

if you are on linux, you can use pkill -f grip

This article may help: https://stackoverflow.com/questions/8987037/how-to-kill-all-processes-with-a-given-partial-name

[HorridModz]

if you are on linux, you can use pkill -f grip

Yes, but it would be nice if grip had built-in functionality that wrapped this.