Enhancement: Convenience Functions

- Bug Fix: build_cross_references() must be able to take into account whether or not the metadata was deleted so that the validate storage functions do not count expired but about-to-be-deleted blocks as orphaned
  - Added appropriate test
- Refactor: removed unnecessary import of httpretty.compat
- Enhancement: Provided an actual implementation for the convenience functions
  - Provided appropriate tests
Enhancement: Test Cleanup Convenience Function

- Refactor: removed some unnecesary imports from the Validation convenience function test module
- Enhancement: Added tests for the Cleanup Convenience function
Merge pull request #9 from BenjamenMeyer/enhancement_worker_functions

Enhancement worker functions