Introduce CSS version checking code.

See ticket DM-1453, CSS code is modified to store version number when
first database is created in CSS in qservAdmin class. All other methods
in qservAdmin check version agains stored version number, same check is
done when css/Facade instance is created. If check fails then
corresponding exception is generated. Version number is defined in two
places nor - qservAdmin.py and css/Facade.cc. Eventually we'd like to
merge that code into one.