Support for UniformSampling and Frame-Skipping

[GokulNC]

This is important for models that take only fixed no. of timesteps as input.

1. Support for UniformSampling

• Rename TemporalSubsample to TemporalSample
• Add a param: subsample_prob
  • If 0 < subsample_prob < 1, randomly sub-sampling or uniform-sampling is done
  • If subsample_prob==0, only uniform-sampling (for test sets)
  • If subsample_prob==1, only sub-sampling (to reproduce results of some papers that use only subsampling)

2. Support for FrameSkipping

• Create a new aug class with param: skip_frames
• Sample once per that value and return

[GokulNC]

We should do this for videos as well as poses.