Remove Script and Package tables. Remove the core.models.script module.
Add the core.models.step module and Step django model.
Add new South migration to change the database accordingly.
Update other references in __init__ and machine for these changes.
	new file:   core/migrations/0012_auto__del_package__del_script__add_step__del_field_machine_init_packag.py
	deleted:    core/models/script.py
	new file:   core/models/step.py

	modified:   core/models/__init__.py
	modified:   core/models/machine.py
Merge branch 'master' of github.com:iPlantCollaborativeOpenSource/atmosphere