Visualization: Improve water / ocean tile rendering

[Flokey82]

Right now we divide every triangle into 3 equally sized shards that are shaded based on the elevation and biome of the region which form the 3 corners of the triangle.

This can mean that the water portion extends to a location on a triangle that is, de-facto, above sea level, which causes issues when mapping the rendered tile on the 3d mesh (heightmap).

We need to improve the way the triangle is divided and rendered to ensure that we only render ocean up to sea level and not any further.

[Flokey82]

Rendering is now improved for rendered tiles when shadows are enabled.

TODO:

• River intercepts at below sea level
• Normal terrain map and SVG export improvements