Don't use a magicgui widget as a global store for attributes

[jni]

Somehow the code evolved to use a magicgui function not for a gui but for its ability to have bound variables, here:

affinder/affinder/affinder.py

Lines 77 to 82 in 393b0c6

	# make a bindable function to shut things down
	@magicgui
	def close_affinder(layers, callback):
	for layer in layers:
	layer.events.data.disconnect(callback)
	layer.mode = 'pan_zoom'

and here:

affinder/affinder/affinder.py

Lines 141 to 142 in 393b0c6

	close_affinder.layers.bind(points_layers)
	close_affinder.callback.bind(callback)

This is generally a gross abuse of magicgui and the Python programming language. 😂 Since the main widget is stateful, the correct thing to do is to make a class subclassing FunctionGui.