Model-agnostic Mapping comparison images

Add 3 images per dataset for the LOD-style comparison slider:

TUM1

• tum1_view1.png — View 1 (e.g. Raw RGB)
• tum1_view2.png — View 2 (e.g. Online Rendered Feature)
• tum1_view3.png — View 3 (e.g. Query result)

Custom dataset

• custom_view1.png
• custom_view2.png
• custom_view3.png

Same aspect ratio for all 3 images in each set works best.