Import: Allow deactivate all products of the provider.

To use before importing new products.

NOTE: New method abstract_import_manager->get_match_col_values includes code that is used in some subclasses.
New feature: Templates correspondences to directly import data.
Import using templates: allow update only some column.
Merge pull request #97 from jorix/i-templates

New feature: Templates correspondences to directly import data.