[modules/xrandr] Add display on/off toggling

This one is a bit tricky:
* Clicking on an active xrandr output will disable it
* Clicking on a disabled xrandr output will enable it -> if
  it is a left-click, it will put it as the left-most display
  if it is a right-click, as the right-most display

Also, it will reload the i3 bars (using a script that allows
you to write custom pieces of an i3 configuration that is applied
conditionally depending on the screens you have).

It goes like this:
* Base config is in ~/.i3/config.template
* Output-specific config is in ~/.i3/config.<screen name>
* Output-specific config when other screens are also active is in
  ~/.i3/config.<screen>-<other-screens-in-alphabetic-order>

For instance:
$ ls ~/.i3
config.template
config.eDP1 -> will be applied to eDP1 (always)
config.VGA1-eDP1 -> will be applied to VGA1, if eDP1 is also active
config.VGA1 -> will be applied to VGA1 (if eDP1 is inactive)

fixes #19

bin/toggle-display.sh

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+
+echo $(dirname $(readlink -f "$0"))
+
+i3bar_update=$(dirname $(readlink -f "$0"))/load-i3-bars.sh
+
+xrandr "$@"
+
+if [ -f $i3bar_update ]; then
+	sleep 1
+	$i3bar_update
+fi