Make qdbusxml2cpp include moc files for the header ("includemocs")

qdbusxml2cpp has a --moc/-m option, but that only tells it to add an #include "filename.moc", ie. the moc file for the implementation file, to the generated file.

What is missing is an option (--includemocs/-M) which includes the "moc_filename.cpp" file, ie. the moc file for the header file, too.

This will become important once we teach cmake or automoc to reject adding includes to mocs_compilation.cpp, in order to enforce includemocs at built time.

Acceptance criteria:

1. qdbusxml2cpp has a new command line option (--includemocs/-M, naming subject to bikeshedding), which will include the moc file for the generated header into the generated cpp file.
2. Use of the new switch is rolled out in at least qtconnectivity and qtbase