12176 attach fsfiles

See: https://trac.openmicroscopy.org.uk/ome/ticket/12176

This PR begins the work of enabling the conversion of pre-OMERO5 attached original files into OMERO5 filesets. The `test_reimport.py` integration tests performs all the steps necessary to perform such a transformation. In order to clean up after the swap, a new command `omero.cmd.ImageBinariesRequest` (name suggestions welcome) was added which for the first time allows for deleting /OMERO/Pixels files (incl. Pyramids) without needing to delete the entire object.

In order to make better use of some existing methods, this PR also refactors:
 * `BasicACLVoter` which will hopefully alleviate some of the `DUMMY` exceptions we've seen on jenkins
 * `getManagedRepository` logic into `omero.client`
 * `write_stream` logic into `omero.client`

Initial "testing" needed is an API review of `test_reimport` for possible inclusion into `5.0.2`. All integration tests should continue to pass. A next step for this PR is likely to include use of the new command into `fs.py`, though that may depend on whether or not the logic in `test_reimport.py` becomes an OMERO user script or something else.