Refactor Controller

[JustinTervala]

the core.controller object is becoming bloated and rigid. I propose that we break it up as follows (pseudocode):

class WorkflowExecutor:
	self.executor = MultiprocessesExecutor()
	self.playbook_store = PlaybookStore()
	self.scheduler = scheduler()

class MultiprocessedExecutor():
	def execute_workflow(Workflow)
	def pause_workflow(workflow_execution_uid, workflow_name)
	def resume_workflow(workflow_execution_uid, workflow_name)
	def _event_callback
		# maybe all execution elements could call a single blinker signal. MultiprocessedExecutor connects that signal. No need for injecting callbacks deep into workflow structure
	def shutdown()

class PlaybookStore():
	self.playbooks = {playbook_name: Playbook}
	self.playbook_loader = JsonPlaybookLoader()

class JsonPlaybookLoader:
	# These may all be static for some loaders. Keep them in a class. Essentially allow module to be used as a field in PlaybookStore
	def load_workflow(resource_location, workflow_name, playbook_name)
	def load_playbook(resource_location)
	def load_all(resource_collection_location)

class Playbook():
	self.name
	self.workflows = {uid: Workflow}
	def as_json()

[JustinTervala]

Of these objects, I think getting a MultiprocessedExecutor object and a Playbook object are the most important.