[mapistore-python][sample.py]: Correct typos, blank lines and white spaces
[mapistore-python][sample.py]: Add message and attachment caches - modifies save and set_properties, which take effect now
[mapistore-python][sample.py]: Rename "message"/"attachment" dictionaries as "basedict" (+clarity and consistency with folder class)
[mapistore-python][sample.py]: Get rid of the temporary dictionaries in set_properties
[mapistore-python]: Correct attach_id behaviour - include ID and next_aid
[mapistore-python][sample.py]: Rewrite some "for"loops
[mapistore-python][sample.py]: Remove trailing commas
Merge pull request #131 from icandigitbaby/mapistore-python-fixes

More fixes in the Python sample backend