Map Ctrl-Shift-F to contact search and Ctrl-F to find
As discussed on <https://bugzilla.gnome.org/show_bug.cgi?id=645121>,
currently Ctrl-F opens the contact search dialog, and there's no
keyboard shortcut for searching within the contact list (other than just
typing). The Gnome HIG handles this situation: it says that the former
should be Ctrl-Shift-F and the latter should be Ctrl-F.
<http://library.gnome.org/devel/hig-book/2.32/input-keyboard.html.en#standard-shortcuts>