New Link Dialog

[Erick Pérez Castellanos <erick red gmail com>]

I've just uploaded the patch [1] for the link dialog to looks almost
like the mockup.

There's some issues still here:
1. What to do when the link operation fails.
2. The button size to look like the mockups, though after some
discussion with Allan this morning, they (the designers) agree that it
should not be done in the app itself, but more like a theme thing.

Now, I think it will need some testing, I've made some, but It will be
better to test more of it.

[1] https://bugzilla.gnome.org/show_bug.cgi?id=657945