Add fake companion file (.fake.properties) (Fix #10993)

Logic for the fake file handling is largely copied from
the DeltavisionReader. To keep this simple, I haven't (yet)
tried to refactor any of that logic into FormatReader.

Properties set in the .fake.properties file override any of
the properties in the filename itself.

/cc @melissalinkert

**NB**: *this is one possible solution for companion files as described in https://trac.openmicroscopy.org.uk/ome/ticket/10993 but happy to address others. I needed companion file creation via fakes for testing another issue. Happy to have this closed for further consideration.*