Matthew Iadanza authored Apr 13, 2023 and Tom Burnley committed Apr 13, 2023

Fixes for issues that came up whilst making the Doppio nodes panel:

- Add `default_results_display` for Image3D nodes in `mrc` format
- Fix errors in `default_results_display` for Image2D nodes
- Make the `default_results_display` for the `Node` superclass `ResultsDisplayPending` rather than `ResultsDisplayText` this way doppio will continue to attempt to update it after creation. 
- Made sure all the thumbnail creation in `mrc_image_tools` checks to see if dirs exit before attempting to create them to prevent errors
- Made sure all `mrc` writing in `mrc_image_tools` has an `overwrite=True` flag, to prevent errors.
- Tests updates for these changes

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