relax SVN archive

Spun out some functions of generic_fns.model_selection into the new lib.model_selection module.

Shifted the generic_fns.xplor module to lib.xplor.

Reverted revisions r19065, r19066 and r19067.

The command used was:
svn merge -r19067:19064 .

The idea of the data_store.control absorbing most of generic_fns is not so good!

Renamed data_store.lib to data_store.control.

This is due to too many clashes with the lib package.

Shifted most of the modules containing data store objects into data_store.objects.

Created two new empty packages data_store.lib and data_store.objects.

The data_store.lib package will be for functions and modules from generic_fns which manipulate the
data store objects, and the data_store.objects package will be for the special objects of the store.

Created the empty lib.chemical_shift package.

Created the empty lib.dispersion package.

Fix for the lib.arg_check module for the shift of check_type module into the lib package.

Moved the check_types module into the lib package.