Merge branch 'merge-preconvert' into 'merge-foundation'

Merge preconvert

Very basic cleanup of some of the mesh conversion infrastructure prior to binging in large pieces of code.

- Remove ancient samm, pro-am, prostar3 routines as being unused and unsupportable (since the original products ceased existence over 10 years ago).
- Open protected access to some meshReader bits, to help when implementing polyhedral readers.
- Drop meshReaders/meshWriters namespace, use fileFormats instead.
- Reorganize file-structure within src/conversion.

See merge request !69