Cleanup of directory layout

[iislucas]

I think there's a bunch of old unused stuff that I'd like to remove and some directory structure I'd like to improve on too:

Cleanup by removing:

• Root level get_revisions directory. See PR: remove unused root get_revisions dir #63
• Root level conversation_reconstruction directory doesn't contain anything currently that I think is in use. See PR: remove unused conversation_reconstruction #64
• conversation_reconstruction_dataflow/ingest_revisions/.dataflow_main.py.swp; Done in commit: f92c785 (oops, I meant to do this as a PR, will setup security so we don't push directly to master in future)

Restructuring:

• I think we should also move the dataflow and local versions of conversation reconstruction into the root level reconstruct_conversations and then they day be reconstruct_conversations/dataflow and reconstruct_conversations/local instead of having three root level directories.