[packagekit] A new update viewer

[Richard Hughes]

A few keen eyed hackers will have noticed a load of new code being
pushed into gnome-packagekit git.

I've been working on a new update viewer, as the old one had lots of
issues:

* Lots of sync calls that make cancelling a pain in the ass
* No size information
* Lots of windows that pop up
* Three pane design that was difficult to maintain, and explain

I've got some prototype code in a local branch here, and the results are
something like this:

http://people.freedesktop.org/~hughsient/temp/gpk-update-viewer2.ogv

Ignore how some sub-bars repeat (backend bug), and also that you need to
do the repo-sig and the eula (this is for testing). I've used the OSX
updater as inspiration. Comments appreciated.

Nothing in git yet, as I wanted some feedback,

Thanks,

Richard.