Multi monitor support

When restarting i3 check for connected second monitor: scale it and
restart polybar if there is one.
Put polybar tray on the main monitor.
Do not kill polybar and relaunch it when restarting i3, but restart it
using ipc (much faster).

.config/polybar/config

@@ -24,7 +24,7 @@ modules-left = i3 pulseaudio xbacklight battery-custom
 modules-center = datetime
 modules-right = vpn wlan bluetooth powermenu
 
-tray-position = right
+tray-position = ${env:TRAY_POS:right}
 tray-detached = false
 tray-scale = 1.0
 
@@ -36,10 +36,13 @@ foreground = ${colors.foreground}
 line-size = 3
 line-color = ${colors.primary}
 
+enable-ipc = true
+
 ;#################################################
 
 [module/i3]
 type = internal/i3
+pin-workspaces = true
 format = <label-state> <label-mode>
 index-sort = true
 wrapping-scroll = false