Merge pull request #131 from icandigitbaby/mapistore-python-fixes

More fixes in the Python sample backend
[mapistore-python]: Implement delete_message (hard deletion)
[mapistore-python][sample-backend]: enable get and set properties for attachments
[mapistore-python][sample.py]: Implement create_attachment
[pymapistore]: include attachment ID in Python bindings
[mapistore-python]: implement ROPSaveChangesAttachment
[mapistore-python][sample.py]: Implement RopGetValidAttachments in OpenChange
[mapistore-python][sample-backend]: Implement move_copy_messages
[mapistore-python][sample-backend]: Implement move and copy folder
[mapistore-python][sample.py: Enforce property usage instead of FID/MID attributes
[mapistore-python][sample.py]: Return MAPIStore errors instead of magic values

- Not necessarily a permanent solution - the MAPIStore Python bindings might stop being exposed in the backend at some point
[mapistore-python][sample.py]: Remove unnecessary return instructions