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
How is this reported back to the user? It doesn't necessary feel like an error to me, more like a bit of info. There may be scenes without geometry that still can make sense to publish right?