Implement and fix InstanceStatusHistory functionality for different instance actions.
	modified:   api/instance.py
Add created_by_identity to Instance, Machine, ProviderMachine and Volume.
Add created_by to Volume and ProviderMachine.
	modified:   core/models/instance.py
	modified:   core/models/machine.py
	modified:   core/models/volume.py
Add initial allocation implementation.
Add initial South migration for adding more created_by and
created_by_identity fields. Still nullable.
Add initial service.allocation rules module.

	new file:   core/migrations/0009_auto__add_field_volume_created_by__add_field_volume_created_by_identit.py
	new file:   core/migrations/0010_auto__add_allocation__add_field_identitymembership_allocation.py
	modified:   core/models/__init__.py
	new file:   core/models/allocation.py
	modified:   core/models/group.py
	new file:   service/allocation.py
Merge branch 'master' of github.com:iPlantCollaborativeOpenSource/atmosphere