script_ui ignores defaults if omero.model objects. See #11243

Don't use script parameter default E.g: ``` default=omero.model.OriginalFileI() ``` to populate the field in the script UI.

To test:
 - Need to show the Make_Movie.py script in web. Need to comment out this script from the excluded scripts in omeroweb/settings.py at this line:
```
'"/omero/figure_scripts/ROI_Split_Figure.py", "/omero/export_scripts/Make_Movie.py",'\
```
 - Now it should show up in the web scripts menu. Choose the script and check that the fields named: Watermark, Intro_Slide and Ending_Slide are blank.