SMW\StoreFactory class (deprecates smwfGetStore())

Code coverage: 100%
CRAP: 5

Using a proper store factory class because having unit tests
rely on smwfGetStore() is bound to fail as one is unable
to alter testing conditions.

smwfGetStore is deprecated with 1.9 and will be removed in 1.11

Change-Id: I3e9506e3fb3495e03911d7248fa66f8eb88f26a7