[Qt5-feedback] Add QtService to Qt proper

[BRM]

QtService is presently only supported via an add-on to Qt. I would be very 
helpful to have it be part of the official Qt instead of an add-on - e.g. it's 
distributed with Qt just like QtGui.
It could also use some TLC, for example:

- QtService is presently a set of template classes, making use of Signal/slots 
hard. It could probably be better done using Abstract classes to define the 
interface.
- It would be useful to schedule shutdown as opposed to having the '-t' option 
simply terminate it; probably '-t' should be "--force-shutdown" instead.
- The "Interactive Service" functionality could probably be removed given that 
(i) adding GUIs to services is not adviced, and (ii) Windows no longer supports 
it (as of Vista). Other platforms may but we probably should follow best 
practices and encourage developers to split the service from the GUI.

Ben