Logistic regression: New API

Changed the API of logistic regression

Also removed the execution mode of some files
Logistic regression: New API, updated user doc & install-check

Also corrected several bugs caused by the previous commit
Logistic Regression: Updated user/dev docs and other comments

Updated the comments and documentation to reflect the new API changes
made in the previous commit.
Added function to handle convergence without grouping
Small typo corrected in logregr_accuracy in validation module
Changed the py_in argument validation
Typo in py_in file
Another typo in validation
Compatibility: Fix install-check error due to logregr missing

Due to the change in logistic regression API change, logregr is
not available any more to test create_temporary_table_as(). This
commit changes that to use linregr as an aggregate to return the
tuples that can be used in compatibility tests.
General CV does not need a wrapper for logregr any more.
Added more checks for table names in argument validation