Added data_cols existence check to general CV
Common utility functions for regularizations

Some useful functions for Ridge, LASSO and Elastic-net.
Make utils_regularization.py_in compatible with array[] expressions
Make utils_regularization.py_in compatible with array[] expressions
Make utils_regularization.py_in compatible with array[] expressions
Linear Ridge regression together with cross-validation support
Ridge linear regression: Make it accept array[]

Also removed some argument validations that are related to the independent
variable, because the independent column name might be an actual SQL
expression
Linear LASSO regression using IGD algorithm

with cross-validation support
LASSO linear regression: Accept array[...] expression

* Used unique string as args column names, so that they do not confuse
  with source table column names
* Made utilities location consistent
* Removed the validation over column existence, because the independent
  column name might be a SQL expression