Unite nodes shaders.
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.
Merge commit '6c98fd6' into merge3

Conflicts:
	client/shaders/leaves_shader/opengl_fragment.glsl
	client/shaders/liquids_shader/opengl_fragment.glsl
	client/shaders/nodes_shader/opengl_fragment.glsl
	client/shaders/plants_shader/opengl_fragment.glsl
	client/shaders/water_surface_shader/opengl_fragment.glsl
	src/client.cpp
	src/mapblock_mesh.cpp