Fix and rename Model.set_current_values_to

The method was broken due to a couple of issues, one being the renaming
of the equivalent parameter function that has been undetected til now
because this method does not have unittest.

* Add unittests
* Rename it to `assign_current_values_to_all`
Merge pull request #357 from francisco-dlp/BUG_FIX_Model_set_current_values

Fix and rename Model.set_current_values_to