Compute shader based pipeline clustering, various fixes

Main

• Port pipeline light clustering to compute shaders
  • Clean up lots of old code
  • Remove all GPU flagging define permutations
• Simplify pipeline interface with new RenderContext struct
• Add a fully customizable shadow pass to the pipeline, allowing for custom shaders
• Improve double click focus in Viewer (#4 (closed))
• Move embedded shaders to separate CMake target and specific folder (#3 (closed))
• Add C++/GLSL-shared globals.hh to pipeline with various defines
• Add CMake option to enable aion profiling for the pipeline
• If ImGui is available, replace periodic log output with profiling GUI in GlfwApp

Minor + Fixes

• Add pipeline markdown guide to docs/
• Remove caching from camera lens, add caching to pipeline StageCamera
• Add new InputState and InputSnapshot class, replacing previous Input class
• Fix pipeline shader compilation on non-NVidia drivers
• Add camera up argument to Handle::setLookAt (#6 (closed))
• Adapt camera move speed to scene AABB in Viewer (#9 (closed))
• Add viewer close on ESC, program termination on Shift + ESC
• Fix SSAO naming
• Add various minor fixes and optimizations