Added PLN Manager (LOCKSS) stubs

refs #5425

Added a Space class for the PLN Manager/LOCKSS.  Functionality relating to
the PLN manager on the changes to the METS file are stubs, since those
requirements not yet decided on.

Updated store AIP and download file functions to work with LOCKSS, and
added a stub callback function for when LOCKSS is done storing the file.
Added a new status for a package for when it is on the Storage Server, but
not yet in LOCKSS.
Rename PLN manager to LOCKSS-o-matic
Update LOCKSS-o-matic fields
Change LOCKSS download URL

refs #5425

Split chunks of an AIP are found at <aip_uuid>/download/<chunk_number>/
now, instead of the chunk number being passed as a GET parameter.
LOCKSS Space can parse service document

Add function to fetch and parse a service document, update the au_size and
collection_iri.  Added dependency on sword2 client library.
Minor fixes

Fix sword2 version, add ipython as a development dependency, and add a
common namespace map for use when working with METS and XML.  Update
existing lxml code to use it.
Create AtoM entry for AIP

refs #6009

Create the AtoM entry with the title, ID, and description of the AIP.
Title and description parsed from the METS file Dublin Core title and
description.  Extract state IRI for polling LOCKSS-o-matic from the
deposit receipt.
Update LOCKSS-o-matic service doc and resource creation

refs #6009

Update LOCKSS handling of service document and atom entries to create
resources to match API changes.

Add checksumType parsing to service document.  Resource creation uses
lom:content tags, add checksum and checksum type to content tags.

Code moved to LOCKSS Space from Package, since it deals more with
Space-specific problems than Package.
Move extraction from a package to the model

Refactored extracting a file from a package to the model, and added a
dependency on atool so it can handle more file formats.  Also, escape the
relative paths coming from the URL.
LOCKSS WIP - edit & state IRI

refs #5425

Properly parse the edit and state IRIs from the deposit receipt.  Add sword
and Lockss-o-matic related namespaces to the namespace map.  Start on
polling for state, comments and logs where work needed.
Initial LOCKSS tests

Add pytest and pytest-django as testing dependencies.  Add testing fixtures
- initial data needed for everything, and a lockss-o-matic specific one.
Start on adding tests; currently only work if the modified simple sword
server is running.