Adding i18n to frontend

[polvoazul]

Lets make an MVP for i18n (internationalisation) of the BD frontend.

Tasks:

• Language selector: as parameter www.basedosdados.org?language=en or in path www.basedosdados.org/en?
• Buy new domains: www.databasis.org, www.basedelosdatos.org.
• Redirects. Example: www.basedosdados.org/precos/en -> www.databasis.org/prices.
• Map calls to metadata variables by language selected.
• Map calls to BigQuery tables by language selected.
• Populate rewrites.
• Add Spanish.

[polvoazul]

It works. We need to define how are we going to select pt/en? Via js var or a field in url? Also, missing url rewriting and localization.

[rdahis]

Superseded by #946. Milestone outlined in https://github.com/basedosdados/website/milestone/6.