[Fix] Multiple changes and fixed related to the way UI system handles srgb

[mvaligursky]

• CameraFrame no long overrides Camera's gammaCorrection and toneMapping settings, but uses those internally for forward passes only, controlled by toneMapping setting of the CameraFrame. This gives us separate control of tonmapping and gamma for the 3D scene, rendered by the CameraFrame, and separate controls for follow up rendering (UI).
• few internal UI textures now correctly use SRGB format
• few example UI textures are also correctly loaded as SRGB
• new HDR example, which has both the 3d scene and UI texture element, and allows CameraFrame to be enabled/disabled and also control over tonemapping for the camera separately from tonemapping from CameraFrame.