- Add more thorough checks to input file quality (check magic word,
  check that all file headers indicate the same packet size and block size,
  etc)

- Add some means of figuring out an informative "active VSN" to send out in DifxMessageMark6Activity
  Library does not care about slots but rather uses path patterns, hence supports off-module data
  copies or unusual on-module layouts also encountered sometimes in practice. These don't necessarily
  have any .meta dirs with group&VSN infos!
  -> add iface for a user specified VSN/string?