DEFERRED_SHADING_DEMO: Add spotlight support
PROJECT: Fix merge error
DEFERRED_SHADING_DEMO: Add a z cull for the final gather
COMMON: Remove storage of ID3D11Device pointer

The only usages are in Initialize, so there is no need to store it
COMMON: Release memory during deconstruction
COMMON: Minor renaming and moving of State classes

To fit the current code style
COMMON: Add memory management to the devices state classes
DEFERRED_SHADING_DEMO: Fix memory leaks
PROJECT: Create README.md