search-view: start searching after 3 characters and 500ms

Add timeout and minimum string length (3 characters) before triggering
searching routine.

App freezes and lags for a few seconds once one starts typing due to
the huge amount of matched events.

Search will be triggered only if passed time since last inserted
charactere is at least 500ms and three characteres have been entered.
If length is already >= 3 but user keeps typing in a quick fashion
(i.e. faster than 500ms per charactere) pre-scheduled search routine
(timeout from the last inserted char) is cancelled and a new one
is created.

https://bugzilla.gnome.org/show_bug.cgi?id=775549

src/gcal-search-view.h

@@ -43,6 +43,7 @@ GtkWidget*     gcal_search_view_new              (void);
 void           gcal_search_view_connect          (GcalSearchView *search_view,
                                                   GcalManager    *manager);
 
+
 G_END_DECLS
 
 #endif /* __GCAL_SEARCH_VIEW_H__ */