Add support to reverse the search_terms to GetFacts

I needed a way to retrieve all tasks that did not have a particular tag - ie.. a NOT for search_terms. I imagine that it may be useful for others.

On a side note to get hamster@master installed on my Ubuntu 12.04 machine I also needed to do the following:

	sudo apt-get install libglib2.0-dev gnome-doc-utils vala-dbus-binding-tool gnome-control-center-dev
	sudo ln -s /usr/bin/vala-dbus-binding-tool /usr/bin/dbus-binding-tool

I'm not sure if this is something that is unique to my installation thus I haven't put it in the README - however I'm pretty much running stock Ubuntu 12.04 with Gnome 3 so I imagine it might be an issue for other users.