Revision 140861

Contributions from Brent Worden - Bugzilla Issue 20279

* a distribution factory following the abstract factory pattern.
The value being, if users want to swap out the default distribution
implementations with their own, why stop them.  The factory is responsible for
create the distribution instances (only continuous ones for now).

* Each distribution has a cummulativeProbabilty method which returns the value of
the CDF for a given value.  By default, via the abstract distribution base
class, an inverseCummulativeProbability method is all provided for all
distributions.  It's implementation is generically handled by applying root
finding techniques to the cummulativeProbability method.  That way, when new
distributions are added, authors only need to create the CDF method and the
inverse is provided automatically.

* Currenty, the only distributions are Chi-Squared and Gamma (one actually since
Chi-Squared is a specialized Gamma) but more are planned.