GUI - switch to GooCanvas2 from Gnome2::Canvas

[shawnlaffan]

Gnome Canvas has been deprecated as long as we have been using it.

GooCanvas seems like a decent replacement, albeit there are not many recent updates to it either.

In any case, Gnome2::Canvas will not work under Gtk3, while GooCanvas2 will. (Issue #770)

To do:

• [ ] Sort out pan and zoom. We are probably using the wrong methods at the moment (world_to_window etc)
• [ ] Get the transforms working. They currently seg fault.

[shawnlaffan]

Look into https://metacpan.org/pod/GooCanvas2::CairoTypes