implemented a clean octree leaf find method
removed uncessary m_qef_{pos,nor}

they were using memory for nothing since we have the same data in the vertex
buffers
fixed a bug that lead to incorrect normal (z borders were missing)
made the code simple (i.e. not per slice) to prepare the next work (lod+per brick)
implemented first part of LOD system for DC
finished first simple implementation of the LOD system
removed bitrot
removed unused distance field ray marching shader
started to implement a crack fill function