Improvements to XML import

[birm]

This is about the xml import utility: https://github.com/camicroscope/caMicroscope/blob/master/apps/port/import.html

• From the xml, the line color under Annotation is a decimal representation of color, read this in
• Sometimes (always?) the xml document is supporting polyline, not polygon. This has confused users who have drawn lines and caMicroscope tries to "complete" the polygon
• Each XML Annotation group should be its own annotation object (toggleable independently)