Add backlog purpose

refs #6131
POST to Location moves files

refs #6131

POST to a Location with information about the source location and the paths
of the files to be moved, copies the listed files from the linked Location
to the Location POSTed to.  Directories are created with 775 permissions
instead of 755.
Add default backlog location

refs #6131

Add config option and default values for a default transfer backlog location.
Allow backlog transfers to be stored

refs #6131

Add support for storing a transfer in a backlog Location when a Package is
created.  Add checks to ensure packages only go to the correct Location's
purpose (ie AIPs go to AIP storage, transfer to transfer backlog). Refactor
store AIP code to share some in common with backlog transfer.  Expect AIP
storage origin_path's to be relative to the Location.
Transfers can be deleted from backlog