Add instance and machine histories using core.models.

Endpoints:
/api/provider/<provider_id>/identity/<identity_id>/instance/history
/api/provider/<provider_id>/identity/<identity_id>/machine/history

Both support pagination using ?page=<num>

Core.models.instance.Instance.hash_machine_alias now has validation and
uses hash_alias if it can't find esh._node.extra['imageId'].

	modified:   api/instance.py
	modified:   api/machine.py
	modified:   api/serializers.py
	modified:   atmosphere/urls.py
	modified:   core/models/instance.py
	modified:   core/models/machine.py
Merge branch 'master' of github.com:iPlantCollaborativeOpenSource/atmosphere