Rework saliency plots to use puma
Summary
This MR introduces the following changes
- Using puma to create saliency plots
- Fix disabled unit test for saliency plots
- Re-implement saliency plots (remove hard-coded stuff)
- Adding docs for saliency
- Removing PyATLASStyle. Umami now works completely with Atlasify
Relates to the following issues
- Closes #176 (closed)
- Closes #155 (closed)