Volocity: flag most files as being pixels files

This is the second part of the fix for #12485.  This should speed up
import time and assist in preventing MemoryLimitExceptions for large
Volocity filesets.
Merge pull request #1289 from melissalinkert/rebased/dev_5_0/volocity-companion-files

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