OHIF support for multi-label scribbles

[masadcv]

Recent updates added multi-label scribbles support to monai label and slicer. To have feature parity with OHIF, similar updates are needed to make scribbles work with recent changes.

This involves (and is not limited to) the following steps:

• Add support in OHIF to work on specific labels within multi-label setting
• Add support in OHIF to communicate segmentation labels metadata (similar to how its done currently in 3D Slicer plugin)
• Properly update/populate segmentation labels in OHIF, given output from a scribbles flow