Conduit file upload method that takes in the files content hash and name. Returns the file phid if successful. Updates to phutil library map.

Summary: Conduit method to upload a a new file using a hash

Test Plan: Try uploading a file using its content hash

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4899