fix #11202: introduce suggestChecksumAlgorithm method to FS API

The main thing to test is that this breaks nothing: imports still work, and SHA1 hashes are still properly noted in the `originalfile` DB table. Also, check that the `ManagedRepositoryITest` unit tests all pass.

--no-rebase as `dev_4_4` is limited to only `SHA1-160`.
Fixes http://trac.openmicroscopy.org.uk/ome/ticket/11202.