Adapt to Qt5 meta-object changes

Adapt to Qt5 meta-object changes

QMetaMethod::signature() has been renamed to methodSignature(), and
it now returns a QByteArray. Also, the new function
QMetaMethod::isValid() should be used to determine whether a method
is valid, instead of relying on signature() returning a 0 pointer.

Where it makes sense, the existing code that was using signature()
and parameterTypes() has been changed to use the new API
QMetaMethod::name(), parameterCount(), and parameterType(int).

Also, in the new meta-object revision (7), the QMetaObject stringdata
member is now of type QByteArrayData*. QFastMetaBuilder will be
ported to generate the new format, but for now it's sufficient to
reinterpret_cast the stringdata assignment to keep it compiling.

Change-Id: Ie340ef17bcebc3afa4aae6450dfe2d06e4d881a4
Reviewed-by: Aaron Kennedy <aaron.kennedy@nokia.com>