47 - replace SailConfiguration with loadable SailFactory's

[joshsh]

At present, all of the code for instantiating various Sail implementations
(MemoryStore, LinkedDataSail, NativeStore, etc.) is in a single
SailConfiguration class.  It's not very extensible that way: it would be
better to have a single SailFactory abstract class and a number of
implementations, so that we can load implementations at runtime.  This
avoids tying Ripple to a fixed set of database dependencies.  The abstract
class will accept a Properties object in order to instantiate a Sail, the
properties used by the particular Sail implementation being specific to
that implementation.

Original link: http://code.google.com/p/ripple/issues/detail?id=47