Adjustments > Photo > Red-eye: additional features, fixes

- User now has control over the eye classifier's shape and size
thresholds (UI for these looks weird; I'll fix it soon)
- Size and shape heuristics work much better now
- Progress bar and messaging is now properly implemented
- Misc clean-up and improvement

Note that the quality is still poor on some photos and there are
additional validation checks that need to be implemented.  These are on
my to-do list.