Tutorials support English and Spanish - #118

I will continue working on this PRs based on the work done by @felixminom .

I will have to pause as the complexity of this PR is too great at the moment. However, I have updated the work done so far.

What works:

• Creation of Spanish and English version routes from the same tutorial file.
• Spanish version of the tags for both english and Spanish.
• Proper Spanish context for this tag indexes given by the html template /es/templates/tutorials-list.html and proper title.

What does not work:

• Tags inside Spanish version of the tutorials link to the English version of the tag indices.

Future work:

• Use a file extension hierarchy to create Spanish and English version of the tutorials (*.es.md and *.md). If a .es.md version of the file is found use that one to create the Spanish tutorial, instead of the .md version.