irsync for python client

[chStaiger]

Hello,

for efficient collection synchronisation, it would be great to have an irsync-like function in the python API. Currently we implemented a workaround which first compares the local folder and the irods collection either by checking sizes or checksums and in a second step updates only those files which differ. However, we cannot easily resume a file upload of a large file, but can only rewrite the whole file. See also: https://github.com/chStaiger/iBridges-Gui/blob/498ad4b0c04b2f482832c5d34dcb92cbc83bc685/utils/irodsConnector.py#L491 https://github.com/chStaiger/iBridges-Gui/blob/498ad4b0c04b2f482832c5d34dcb92cbc83bc685/utils/irodsConnector.py#L546

It would be great to have a more efficient way to implement this functionality.

[trel]

related to #276