Implement proper systray integration for Mac OS

[diederik]

When KMess hides to the system tray, it displays a warning message that KMess remains active. For Mac OS, we don't have to display this message. When a window is closed, the app always remains active in the dock.

Like Adium, we should change the KMess icon to display the status in the dock icon itself. The notification message can be removed.

[valerio]

@Sjors: Is this done?

[sjors]

Not nearly enough, the Dock icon does not act like other Dock icons do...

For example, upon clicking it the KMess main window should pop up if no windows are active; if windows are minimized they should come up. I don't think this happens at the moment. The notification is not displayed because taking a screenshot is not supported on non-X, so incidentally that works, but the warning at compile-time should be removed.

Maybe there are some other things that need fixing to make this 'feel right', but those will only pop up in my mind when the above things are fixed and I try to do things that don't work in kmess, but do work in other applications...