`depthWrite` material property

[gchoqueux]

Warning, when depthWrite material property is set to false, it could generate rendering issues. For instance, an object with this property could erased by an object behind.

These layers could have this issue :

PointCloudLayer

OGC3DTilesLayer

[Desplandis]

@ftoromanoff

[Desplandis]

Removed by #2584. We will have to find another way to fix rendering issues when hiding classification classes.
@AnthonyGlt @ftoromanoff This was what caused issues with pointclouds in #2561.