MONAI Label: Add OHIF+Orthanc Tutorial/Doc (#1149)

The OHIF + Orthanc + MONAI Label spleen segmentation tutorial.

Key features:

- OHIF installation and setup
- Orthanc installation and setup
- Sample data preparation
- MONAI Label plugin
- auto-segmentation with MONAI Label and OHIF
- How to annotate images
- Model training
- Active learning

Signed-off-by: tangy5 <yucheng.tang@vanderbilt.edu>

Author: tangy5