Rewrite Camera, add CpuTimer, various fixes

Camera

• Extract projection logic into new class Lens
• Extract positioning logic into new class Handle
• Rewrite Camera, now just a thin class containing Lens + Handle, with some passthrough
• Rewrite smoothing logic to fix orbiting
• Addresses #4 (closed) and #5 (closed)
• Extract camera utilities to free functions in CameraUtils

Timing

• Add CpuTimer, a simple, <chrono>-based timer
• Replaces PerformanceTimer in GlfwApp
• PerformanceTimer deleted

Pipeline

• Fix uninitialized members in StageCamera
• Fix shadow acne by reintroducing depth biasing
• Add 3D LUT-based color correction