doc (gallery): quickflat

[fatmai]

• [x] curvature.py
• [x] cutouts.py
• [x] dropout.py # FIXME: convert code block in docstring to LaTeX
• [x] rois.py # showing / displaying rois on quickflat plots
• [x] sulci.py
• [ ] extra_layers.py
• [ ] custom_toppings.py
• [x] colorbar.py
• [x] make_png.py
• [x] make_svg.py
• [ ] make.py
• [ ] thickness_mapping.py

[fatmai]

#202