25946 Mari support

- Added Alembic Cache publish to Maya secondary publish hooks
- Added Mari publish hooks and functionality to export texture channels & layers
- Fixed resizing issue in items list
- Unrecognised items returned by the scan-scene hook are now ignored - previously they would raise an exception
are we planning on adding more stuff here? Or are we expecting users to extend  this with their custom validation? Maybe a few more comments to clarify would be nice!