#42 Hierarchical Voxelization : Mipmapping

- added Compute Shader for mipmapping a voxel grid texture into the next
coarser level
- added Dispatcher to work on a voxel grid
- added Interfaces in program cycle to dispatch mipmapping
- added key press listeners to in/decrease visible mipmap level
#41 Revising Code : Renamed Shadow Mapping App

- renamed to transmittance shadow mapping, since that's what it is
- added pointer to texture level int to Overlay RenderPass
#41 Revising Code : Renamed Shadow Mapping App 2

- follow up to last commit