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/scene/types.ts

@@ -16,4 +16,4 @@ export interface Scene {
   elements: ExcalidrawTextElement[];
 }
 
-export type ExportType = "png" | "clipboard" | "backend";
+export type ExportType = "png" | "clipboard" | "backend" | "svg";