The previous commit broke activation when selecting an actor
from a custom renderer. Fix this by explicitly defining a method
activateSelected on the search renderer.
The high level goal is to separate the concern of searching for
things with display of those things; for example in newer mockups,
applications are displayed exactly the same as they look in the
AppWell.
Another goal was optimizing for speed; for example,
application search was pushed mostly down into C, and we avoid
lowercasing and normalizing every item over and over.
https://bugzilla.gnome.org/show_bug.cgi?id=603523
