Textures for relief/bridges/waterbodies in CityTiler

[LorenzoMarnat]

Create textured 3DTiles of relief, water bdies and bridges (see issue). The main problem seemed to be in our 3DTiles viewer UD-Viz and was fixed in this PR.

This PR reduce the computation time of textured 3DTiles with the CityTiler.

• Choose the object type (buildings, relief, etc) with --type flag
• Add textures to water bodies
• Query texture images only once per tile. We used to query the same image a lot of time when many surfaces shared a texture