Update: restore workflow_type WorkflowExecution's attribute

+ In order to enhance and boost metrics collection,
WorkflowExecutionQuerySet will return WorkflowExecutions
which workflow_type attribute is set. New http request has
been avoided.
Merge pull request #30 from hansotronic/master

record marker failes because markerName is not added to recordMarkerDecisionAttributes
Enhance worker actor polling error handling
Enhance unknow resource errors management
Merge pull request #31 from botify-labs/feature/refactor_error_management

Feature/refactor error management
Enhance swf errors wrapping via an exception helper
Update worker and deciders actors to use SWFError subclasses exceptions
Merge pull request #32 from botify-labs/feature/further_error_handling_refactoring

Feature/further error handling refactoring
Version bump 0.1.31
Merge branch 'release/0.1.31'
Merge branch 'release/0.1.31' into develop
Merge branch 'develop' of github.com:botify-labs/python-simple-workflow into develop
Merge branch 'master' of github.com:botify-labs/python-simple-workflow

Conflicts:
	swf/__init__.py
Merge branch 'develop'
Update SWFError with a formatted type
Merge pull request #27 from botify-labs/refactor/restore_workflow_type

restore workflow_type WorkflowExecution's attribute
Update exceptions.SWFError: make raw_error optional and sanitize its value
Merge branch 'develop'
Bump version to 0.1.32
Fix actors.worker: import missing exceptions