Created separate package for factor objects.

Moved Factor, ProbFactor, ProbFactorMaker, Semiring, and Variable into
the new Package.

Combined ProbFactor, and ProbFactorMaker into a single Factor file
consisting of an abstract class Factor and a companion object that acts
as a factory. ProbFactorMaker was included as the trait FactorMaker.

Factor was renamed to MappedFactor was modified to extend Factor.
Use new factory to make (create) a Factor
Changes imports to reflect package change
Use factory to make (create) Factor
Use new multiply method (renames product)
Used new factor to make (create) Factors
Fixed firstConting warning
Use new factory to make (create) Factors
Change imports to reflect new packages
Use factory to clear cache
Moved classes to new factor package