deviceStates: Add support for device states in ari-py

This patch adds support for the ARI deviceStates resource. This includes
a sample-api resource as well as a very basic unit test for using PUT
to create/set the state of a device.
Merge branch 'blinky-lights' of git://github.com/asterisk/ari-py

Closes #1.

Signed-off-by: David M. Lee <dlee@digium.com>

Conflicts:
	ari/model.py
	ari_test/client_test.py