Disable deep copy of nested object, allowing to change properties of instances inside classes after their instantiation

[giacomomarchioro]

The user can now change the values of the IIIF object after it has been instantiated using the reference to the original object.

from iiif_prezi3 import Canvas, Manifest

originalID = 'http://iiif.example.org/TESTORIGINAL'
amanifest = Manifest(id='http://iiif.example.org/prezi/Manifest/0', type='Manifest', label={'en': ['default label']})
acanvas = Canvas(id='http://iiif.example.org/prezi/Manifest/0/canvas/01', type='Canvas', label={'en': ['default label']})
asecondcanvas = Canvas(id=originalID, type='Canvas', label={'en': ['second label']})
changedID = 'http://iiif.example.org/TESTCHANGED'
amanifest.items = [acanvas, asecondcanvas]
# we change the id of the first canvas
acanvas.id = changedID
amanifest.items[0].id, changedID

This should fix: #35