Shuffle around some menu related code from window manager into menu
manager. This still is not perfect, and results in a little more of the
window manager to be publically exposed - but this is another step
towards better seperation of concerns between menu and window manager.
We also move the mouse_event handling into a new function in menu manager
as event handling was beginning to become a bit chunky.
Move applet logic to the own class. Remove applet code from MenuManager.
With new AppletManager applet order is configurable via WindowManager.ini file.
