Signed-off-by: Craig Robbins <kde.psych@gmail.com>

CNodeDefManager::get()
VoxelManipulator::addArea()

getTileInfo() ~1.5x faster
getSmoothLight ~2.0x faster

- Don't create and cache an extruded mesh for every (non-node) item.
  Instead use a single one per image resolution.

- For cubic nodes reuse a single wield mesh too

- Improve lighting of the wielded item

- Increase far value of wield mesh scene camera, fixes #1770

- Also includes some minor refactorings of Camera and GenericCAO.

sky.cpp: m_bgcolor.getAlpha() was being used before initialised

mesh related: m_highlight_mesh_color was being used uninitialised

Pass light sources in blue channel of vertex color instead of decoded light for all special drawtypes.
Plus some style fixes and optimizations.

Skip shading for lightsources and top of the nodes.
Fixes liquid sources and flowing surfaces having different brightness.

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.