Change the return value of QObject::connect

Change the return value of QObject::connect

From a bool to a handle to to connection.

Also added a new overload of disconnect that disconnect a handle

This is required because with the new syntax taking lambda or functors,
it is the only way to disconnect a connection (as it is impossible to
compare functors)

The new return value is QMetaObject::Connection, it is a wrapper around
the internal QObjectPrivate::Connection.
QObjectPrivate::Connection is now reference counted.

tst_qglobal.cpp:
   This test set up an internal callback, and the callback do not set any
   proper connection handle (and tbh,  it would be hard for it to do so).
   So the returned QMetaObject::Connection is invalid, and ok is false
   (Internal callbacks are only used for jambi and should probably be removed)

Change-Id: I111626fb4f47efc4db5e2ea5bff9da15f08fea7b
Reviewed-by: Bradley T. Hughes <bradley.hughes@nokia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>