3D buddy

This branch includes full support for thew new 3D ROI structure.

- Updates to user interface
- Toggling of base image z-plane with mouse scroll
- Full support for v1 sima.ROI.ROI structure
- Registration of 3D datasets and ROIs
- Creation of multi-plane ROIs
- Added support for drawing circular ROIs
- Still need to implement a tool for drawing multi-plane ROIs more easily.  At the moment, assignment of a shared 'label' attribute to polygons in different planes will result in creation of a multi-plane ROI.