Pass drawtype and material type to shaders.
Move shaders generation to startup only.
Allow assign shaders per tile.
Initial code to support water surface shader.

Parallax mapping with slope information.
Overriding normal maps.

Fix Result of processed Request was written to invalid (non existent) ResultQueue if requesting thread timed out before

Also write something about rebuilding shaders to infostream in
Client::afterContentReceived()