[Ayatana] Lenses need a method to provide attribution for APIs

[Stefano <stefano.palazzo@xxxxxxxxx>]

It seems that a lot of lenses are going to use various web APIs, some of which require attribution.

My hypothesis is that people will start to abuse features, such as groups, to provide attribution when they must. It should therefore be a good idea to provide hooks to solve this problem.

My initial suggestion is something like this:

    model.set_attribution_image(url, text)

A mock-up of how this could look: http://i.imgur.com/uhucj.png

What do you think?

- stefano