opti: contextual load for textures

[NickKhalow]

Currently we hold many textures that are used only in certain places and are staled in memory most of their lieftimes: loading screen, camera grid, pad-lock sprite (small sprite takes 7 mb btw) and e.t.c, it could save ~100 Mb with ease

Solution: load required texture in memory when they are needed and offload them respectively

Preview texture is another good candidate to shrink at least by half:

• disable depth buffer since it's UI
• R32G32B32A32_SFloat, instead of it we may consider lighter formats with/out HRD support
• mipmaps can be disabled - we need only one size of texture