Convert classes to interfaces

[esodan]

Currently all implementations are classes, but this will be a problem for external implementations of Items and Shapes, so I think they should be converted to Interfaces and actual classes convert (by renaming) them to default implementations.
Example:
public interface GtkCanvas.Item : Object, Actor {
public signal void selected (Clutter.ModifierType modifiers);
(.. convert to abstract or virtual methods)
}
/* Current GtkCanvas.CanvasItem could be renamed to GtkCanvas.GcItem */

Why?

Because I'm implementing GSVGtk with objects to draw SVG images and shapes, so libgtkcanvas can add classes derived from GSVGtk ones and implementing libgtkcanvas interfaces, so it will get SVG shapes for free.

[Philip-Scott]

I made a channel on slack so we could discuss this :)

If you could help us out with implementing your GSVGtk library so we could render SVGs that would be sweet! That's one of the mayor blockers before we can get an MVP of the library