Ref NeRF Reproduction

Ref NeRF is incorporated successfully (with mip NeRF 360 proposal network distillation). In the previous commits, MSE was not used for PSNR computation (which leads to low PSNR value), and is currently fixed. Current model results in a PSNR of 28.5 (helmet, trained for 7.5 hours) and ~22 (car, trained for 43min)