Add idle-inhibit

Sometimes I don't want the computer to go to sleep bacause I'm
running something in the background. for that I always used
systemd-inhibit sleep 999999 manually on the terminal, but I want
it to be easy to use without remembering the whole command every
time.

Therefor I added a custom button to waybar which does that for me.

waybar/style.css

@@ -81,7 +81,8 @@ window#waybar {
 #window,
 #custom-power,
 #language,
-#mpd {
+#mpd,
+#custom-idle-inhibit {
 	margin: 8px 2px;
 	padding: 0 18px 0 18px;
 	color: black;