Toggle all visible layers in 'layer editor' to Referenced/None state

Referenced_toggle.py

layers = cmds.ls( type='displayLayer')
global chLayViz

#Checks if 'chLayViz' variable exists and if not - assign 'None'
try:
	chLayViz
except NameError:
	chLayViz = None

# Assign toggle value to 'chLayViz' var
if chLayViz == 0 :
	chLayViz = 1
elif chLayViz == 1 or chLayViz == None :
	chLayViz = 0
	
# Check all visible layers and toggle the 'Referenced' state
for l in layers[1:]:
	if cmds.getAttr( l + '.visibility') == True:
		if chLayViz == 1:
			cmds.setAttr( l + '.displayType', 2)
		elif chLayViz == 0:
			cmds.setAttr( l + '.displayType', 0)