Simplify apoint_switch_notify()

Pull out code from apoint_switch_notify() -- especially the fallback
routine that calls recur_apoint_switch_notify() if the currently
selected item is a recurrent item -- and move it to a wrapper function
day_item_switch_notify().

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/calcurse.c

@@ -311,7 +311,7 @@ int main(int argc, char **argv)
 
     case KEY_FLAG_ITEM:
       if (wins_slctd() == APP && apoint_hilt() != 0) {
-        apoint_switch_notify();
+        day_item_switch_notify();
         inday = do_storage(0);
         wins_update(FLAG_APP);
       } else if (wins_slctd() == TOD && todo_hilt() != 0) {