[Upstream PR #33-35] iSpin.tcl updates

## Upstream PRs
- https://github.com/nimble-code/Spin/pull/33
- https://github.com/nimble-code/Spin/pull/34
- https://github.com/nimble-code/Spin/pull/35

## Summary
Various updates to ispin.tcl (GUI interface).

## Status
- [ ] Review PR changes
- [ ] Test implementation
- [ ] Evaluate for inclusion in fork