Store ROIs as vertex lists instead of SVG borders.

[jamesgao]

ROI membership is currently determined by rendering the SVG, and masking the points. This is potentially lossy, as different rendering engines or even different rendered sizes may cause divergent vertex membership.

We propose to use a static list of vertices as the ROI instead of purely SVG based ROIs. This list will be stored in a Dataset which contains all the ROI data as well. Connector scripts will generate either blender files or svg files for editing in Inkscape and Blender, then changes will be imported.