Restructure Regression to use folders.  Make dense Beta function match S...

...parse

This restructure places the attributes into a Folder structure.  Regression/Dense and Regression/Sparse.  Attributes then become OLS (virtual, most of the implementation), OLS_LU and OLS_Cholesky for the decomposition methods.

Signed-off-by: johnholt <john.d.holt@lexisnexis.com>