Add support for rendering template images in SNRHUDButtonCell

[js]

Calling super seems to do an OK job of rendering template images, still not sure about other kind of images and the various imagePosition. Also added a little square button with the builtin NSAddTemplate to the Catalog app.

[js]

sigh, actually now that I look at it a bit closer it is a bit on the dark side as there's not much difference between its disabled and enabled state?

[indragiek]

I think we should be relying on NSImageCell to draw template images instead of expecting super to behave the way we want. I think I tested this earlier and ran into some issues, I'll give it another try soon. In the meanwhile you could try investigating that to see if it does a better job :)