Spanish translation update

This translation has been firstly updated with the new tool [`translations.py`](https://github.com/sagemath/sagenb/blob/master/util/translations.py) and then manually revised and completed. For this reason the [first commit](https://github.com/migeruhito/sagenb/commit/5e5a43c9c805e6f6137601f8178ce84a9d474293) has a very big changeset, but I have only updated the previous version with the tool, I promise.