Rather than converting the dependency graph to a bitmap image,
it is more advantageous to use the vector SVG format and open it
in a web browser (any modern browser supports the format), because
it allows text searches within the image.

This patch adds a new operator and button that does just that.

Differential Revision: https://developer.blender.org/D15325

See T95597

Useful for developers, technical users and TD's.

Works for both 2.7x and 2.8x series. In 2.7x series new tools are to be found in
the Scene buttons, Dependency Graph panel. In 2.8x this panel is in layer
buttons.