Volocity: flag most files as being pixels files (rebased onto dev_5_0)



This is the same as gh-1267 but rebased onto dev_5_0.

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This is the second part of the fix for https://trac.openmicroscopy.org.uk/ome/ticket/12485.  This should speed up import time and assist in preventing MemoryLimitExceptions for large Volocity filesets (e.g. QA 9407).

MemoryLimitException on import may be difficult to reproduce now, so the next best thing is to verify that fewer companion file annotations are created during import with this change.