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.
Some apps (looking at you, VisualBuilder) don't specify an icon
in their .af file, so WindowServer was trying to open an empty path.
That made it print a perror message to the log each time. Let's not
do that ^)
