Integrate UPnP support with the file transfer code

[diederik]

The code for UPnP support has been written some time ago, but it was never implemented in the file transfer code. It's time to do this for 1.6.

There are some tasks to take:

• Update the classes to use the SOAP-call style like the other SOAP classes do (use HttpSoapConnection as base class of UPnP::Service).
• Get rid of the SoapMessage class (code cleanup)
• Make sure the UPnP-discovery code runs before the file transfer invite code (e.g. when the user logs in).
• Add smart handling of the port-mappings, e.g. re-use one when possible, leave a mark it was created by KMess, automatically clean up the mappings.
• Add the settings, see ticket #22

It's possible to implement the networking code first with kmess --runtest upnp.