Make console available in main menu

The problem was a more general one, namely `BindButtonEvents` were not received while the menu is open. The reason was that the keyEvent method in `NUIManagerInternal` consumes key events, if the displayed screen is modal, even if noone really consumes the event.

My straight-forward solution was to simply not consume the event and just stop further processing the event. The bindEvent method of `NUIManagerInternal` still consumes the event, if the priority is equal or lower than `PRIORITY_HIGH`.

Also added two `toString()` implementations to make debugging easier.