Switch to SVG polygons for drawing a SelectionView.

Adds an SVG overlay that takes no pointer-events,
and uses a polygon element inside to it draw
selections with stroke and fill of the user's
color.
Removes the 3 divs used previously.
Merge pull request #265 from adityab/polygon-selections

Switch to SVG polygons for drawing a SelectionView.
Support hyperlinks being added to a document after load

Also added a few hyperlink helper methods into OdfUtils.js
Added hyperlink support for text elements
Added editor buttons for applying or deleting hyperlinks