Adding a support to CholecTrack20 dataset on a new branch cholec

[nwoyecid]

This pull request is to add a support for CholecTrack20 dataset. The modification includes:

1. TrackEval/doc/CholecTrack20-format.txt : Added a new text file describing the result file format.
2. TrackEval/trackeval/datasets/cholectrack.py: Added a new python that create a class CholecTrack2DBox() which extends the _BaseDataset() class. This class prepares the results files and ground truth files in the format needed for TrackEval run.
3. TrackEval/scripts/run_cholectrack20.py : Added a new python file to excute the tracking evaluation on CholecTrack20 dataset.
4. TrackEval/trackeval/datasets/init.py: Modified the file to include a line which imports the cholectrack dataset class defined in 2 above

DATASET INFO:

CholecTrack20 is a surgical video dataset for tool tracking in laparascopic cholecystectomy surgery.
This dataset is annotated for multi-perspective multi-tool multi-class tracking.
Multi-perspective - track across multiple temporal views of tool trajectories (e.g. intraoperative, intracorporal, visibility)
Multi-tool = multi-object
More information on the dataset can be found here https://arxiv.org/abs/2312.07352