Implement methods for saving/loading RegionOfInterest objects to file

[niksirbi]

In #617, I've drafted a napari widget for creating regions of interest as shapes, and assigning names to them. This widget is currently missing Save/Load buttons, because we have no way to natively save/load movement ROIs to disk.

One idea would be to implement two methods in the BaseRegionOfInterest class:

• .to_file() / save()
• from_file() (can be a constructor) / load()

There's is also the question of which file format to choose for storing ROIs on disk. I've discussed some options in a zulip topic: #Movement > Format for storing ROIs to disk.

I've planned to tackle this issue myself this fall, as part of the larger #378 effort.