GitLab

Change structure to provide archival methods in DCCArchive instead of DCCSession; lots of other fixes

- Merged abstract class with DCCSession in sessions.py
- Provided archival result class to hold useful stats
- Added DCC number type validator in CLI

- move exceptions into separate module, and simplify
- pass session object between DCC operations to handle cookies globally
- store archive on file system rather than in memory
- add serialisation/deserialisation routines for DCCRecord
- remove DCCDocId object; just use DCCNumber (now that DCC provides full numbers in XML response)

- updated to Python 3.8
- simplified most code
- separated code into more logical modules
- use ciecplib to handle Kerberos authentication instead of directly

Allow updating DCC metadata

See merge request !3

comms.py: add support for posting the DCC "Bulk Modify" form
patterns.py: add a parser for DCC's response to metadata updates
__main__.py: add CLI for metadata updates