[mapistore-python][sample-backend]: implement delete_message (hard deletion)
[mapistore-python][sample-backend]: Implement move and copy folder
[mapistore-python][sample.py]: Use list and dictionary operations instead of for loops
remove destructors
[mapistore-python][sample.py]: Correct for loops (esp. naming)
[mapistore-python][sample.py: Enforce property usage instead of FID/MID attributes
[mapistore-python][sample.py]: Add breaks (only one message/attachment with the same ID can exist in the "message"/"attachment" list)
[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