Curation UI: Mask section updates

### Description
Update the following (need discussion)
- [ ] separate the sorting section and mask section with a text row said "OPTIONAL"
- [ ] pull out the base layer selection outside of Optional section - need design (dim if user select "no" - not using image, have Seg 1 by default) - might be the required for a task in this ticket https://github.com/AllenCell/allencell-ml-segmenter/issues/262
- [ ] Remove the "Propagate" button (currently non-functional)
- [ ] Revisit the "Finish" state of the [+Create] button - remove if not needed

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### Size
M?

### Additional notes
V1 deliverable??