[packagekit] new method: GetPackages

[Richard Hughes]

I've added a new method into the API:

GetPackages(string=filter)

Basically, it should return all the packages available or installed
(depending on the filter) without any search matching being done.

The common use case will be with an "installed" filter, but we should
probably support all the filter options like basename, gui and newest if
possible.

It should be pretty easy to add, so backend dudes please get coding!

Thanks.

Richard.