doc (gallery): webgl

[fatmai]

• [x] single_dataset.py
• [x] multi_dataset.py
• [ ] animation.py
• [x] static.py
• [ ] static_with_stimulus.py
• [x] static_with_custom_template.py
• [x] interactive_with_custom_template.py
• [ ] interactive_with_picker.py
• [x] save_3d_views.py
• [ ] movie_dataset.py
• [ ] custom_overlay_texture.py
• [ ] custom_webgl_additions.py