Add texture preview options

[Puxtril]

Right now the texture preview is pretty bare. There are a couple image formats that could really benefit from adding 1 or 2 options.

• All previews currently have an option "Apply Alpha", but this should only be shown in textures that actually have an alpha channel.
  • Many textures in /Lotus/Interface/Icons have alpha (Texture package)
• BC6/HDR textures are currently previewed, but the exposure is statically set to a range that makes the preview almost useless. Ideally an exposure slider would allow the user to tweak manually for each texture. https://learnopengl.com/Advanced-Lighting/HDR
  • Ex: the HDR textures in /Lotus/Levels/JadeShadows/JSElevator04 (LightMap package)
• Low-resolution textures should be previewed in their original resolution (not scaled up with the window).
  • Ex. *_mm.png textures, like /Lotus/Levels/JadeShadows/JSElevator04/LevelCapture_mm.png (LightMap package)