Don't unload icons for objects who's icon never changes

Being on a slow internet connection I realised web search icons were re-loading ever time the interface was opened/closed.

I noticed that these types of objects (and others after thinking about it) never need to reload their icons, so I've changed the code in a few places to set `retainsIcon` to `YES`.
Incase you're wondering, the flag is slighty misleading, it doesn't mean the icon is retained (retain count goes up by 1) but just that it's not released. When the object is dealloced the icon is of course still released.