[Do not merge] example of using LibriSpeech + Lhotse Shar

[pzelasko]

This PR shows how to use Lhotse Shar data format to train models in Icefall. I only added the necessary adaptation to the basic TDNN LSTM recipe as I don't have a free GPU at hand to run anything bigger. If it's useful, feel free to adapt this to more recent recipes (very little change is required as most of the changes come inside the datamodule).

[danpovey]

We will try to apply this to other recipes and see what performance improvements we get.