More work on zoom
More work on zoom

I'm moving the overlay rect to the back of the svg element to ensure the
full SVG canvas is covered and setting the zoom handler on the whole SVG
element. This seems to work better when trying to capture events from
elements in the SVG.

rwl/dagre_charted,git-ashish/dagre-d3,cpettitt/dagre-d3,git-ashish/dagre-d3,9n/dagre-d3,cbfx/dagre-d3,dominiek/dagre-d3,9n/dagre-d3,rwl/dagre_charted,dagrejs/dagre-d3,ENCODE-DCC/dagre-d3,9n/dagre-d3,cpettitt/dagre-d3,dominiek/dagre-d3,ENCODE-DCC/dagre-d3,dagrejs/dagre-d3,dominiek/dagre-d3,cpettitt/dagre-d3,cbfx/dagre-d3,git-ashish/dagre-d3,cbfx/dagre-d3,rwl/dagre_charted