I should be able to *easily* invite people I share other Spaces with

(User Story, Closed -> Fixed, Priority: High, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Invites
Summary: While Querki isn't a social network per se, I am finding that I want to be able to invite, eg, Chad into a Space simply by typing "Chad". The system knows that he is in other Spaces with me; it should be able to suggest him as an option.