Refactored and (mostly) Tested WorkflowManager.export()

Had some problems fully testing with mock. See comments in test_workflow.
Implemented and Tested WorkflowManager._interval_ngrams()

Only one more method remaining.. until interval n-gram analysis is done...
Cleanup in other_tests/test_workflow.py

Removing unused mocks and things.
Implement WorkflowManager._variable_part_modules() with Tests

Yay!