Regional spot visualisation tweaks

[vreuter]

• [x] Specify subset of positions
• [x] Combine timepoints
• [x] Use different filtered spot ROIs files (unfiltered, proximity-filtered, proximity- + nuclei-filtered)
• [ ] Include background-subtracted image if available
• [ ] Include transformed image file if available (i.e., for DoG detection method).
• [x] Interrupt and check interactively, or save a small sample and check post-hoc
• [x] Allow position in z to alter bounding box / ROI color for projections in 2D

[vreuter]

Successor to #63