Fixes a six-year-old bug in presets::VolumeRenderingStage which caused rendering artifacts at specific angles when rendering strongly anistropic volumes. There was a work-around previously implemented which, however, was not 100% reliable, and came at the cost of forcing a sample rate twice as high as specified. Since this work-around has been removed now, the specified sample rate is used (which effectively is twice as low as before). This means that same rates must be doubled to yield the same results as before (note that the effective sample rate will be the same then, meaning that rendering performance will be the same, in terms of both quality and time, but without the artifacts). The static field presets::VolumeRenderingStage::DEFAULT_SAMPLE_RATE has thus been doubled.

Fixes bug which may have caused volume data being rendered slightly displaced due to padding (up to one voxel).

• Added presets::MaskRenderingStage.
• Added base::math::computeFastGradient3f.
• Renamed most occurances of "intensity volume" in attributes/fields/methods to "intensities" to be more consistent with "normals".

• Refactored base/Vertex.h and renamed base::VertexBase to base::PVertex.
• Added base::VertexPosition and base::PNVertex.
• Added the solid material shader.
• Added base::IntensityVolumeUInt16, base::IntensityVolumeUInt8, and base::BufferedIntensityVolume.
• Marked base::HUVolumeUInt16 as deprecated.
• Internally, Carna is now intensity-based and not HUV-based any more (since image intensities are a more general concept).
• HUV is still supported and base::HUV is now a class.
• base::math::frustum4f now takes the full FOV angle (not the half).

• Linked GLEW statically into the project by included the corresponding source files, since this is the recommended method.
• Added the BUILD_EGL build switch to build GLEW with EGL support (defaults to OFF).
• Added base::MeshFactory::createBall.