Migrate QByteArray over QArrayData.

Migrate QByteArray over QArrayData.

For the time being QByteArrayData keeps its independent existence, for
the sake of other modules. Once they have been ported to use the new
initializer macros it can be changed to:

    struct QByteArrayData { QArrayData array; };

Extra braces can then be added to the macros.

With respect to source compatibility, the only concern is with other
modules, as QByteArrayData has already changed in incompatible ways with
Qt 4.x

Done-with: João Abecasis
Change-Id: I044e2a680317431777a098feec8839a90a3d3da3
Reviewed-by: João Abecasis <joao.abecasis@nokia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>