add visualizations

[kaczmarj]

we should add visualizations for the different steps in our process... what should they be? some initial thoughts

• [x] segmentation outputs overlaid on the slide region (make the segmentation outputs slightly transparent)
• [ ] tumor vs non-tumor patches on the slide region
• [ ] biomarker positive vs negative patches on the slide region. use various thresholds for biomarker positive.

[kaczmarj]

for visualizations, it could be useful to implement a cv2-like method to add pieces to existing images. like a method to add tumor edges to a cv2 image, and a separate method to add cells, and a separate method to add lines from cells to tumor regions.