SVG export (#598)

* first draft of export to SVG. WIP

* enabled text rendeing - which is not quite right atm

* placeholder svg icon

* size the canvas based on the bounding box of elements

* Do not add opacity attributes if default

* render background rect

* Ensure arrows are in the same SVG group

* parse font-size from font

* export web fonts

* use fixed locations for fonts

* Rename export functions

* renamed export file

* oops broke the icon.

src/utils.ts

@@ -1,3 +1,5 @@
+export const SVG_NS = "http://www.w3.org/2000/svg";
+
 export function getDateTime() {
   const date = new Date();
   const year = date.getFullYear();