Wrapper improvements for ROIs

[Tom-TBT]

Changes in this PR are to increase the support of functionalities around ROIs:

• support annotations on ROIs (could be used to organize ROIs with tags, add properties with KV pairs, ...)
• getShapes for an ROI now retrieves wrapped shapes instead of ShapeI

[will-moore]

It is a nice improvement for roi.getShapes() to return ShapeWrapper instead of ShapeI but it is unfortunately a breaking API change.
Although roi.getShapes() isn't really documented or used in our examples, it is currently mapped to roi._obj._getShapes() and it's possible that users have code that would break with that change.

I noticed that _RoiWrapper has

    # TODO: test listChildren() to use ShapeWrapper? or remove?
    CHILD_WRAPPER_CLASS = 'ShapeWrapper'

And roi.listChildren() fails, since this expects a link class such as ProjectDatasetLink etc.
So you could rename your getShapes() to listChildren() and remove the CHILD_WRAPPER_CLASS = 'ShapeWrapper'.

To be consistent with other listChildren() behaviour, IF the shapes aren't loaded then they should be loaded on the fly (and probably cached) as we do in some other places.

[will-moore]

Could you also add support for loading Shapes on the fly in listChildren() if they're not already loaded?