Manual adjustments to numpy.org Spanish translations

[steppi]

This PR enables Spanish translations and contributes some manual fixes to #774. The numpy.org content was translated to Spanish within Crowdin, and typically manual adjustments are needed to get the documentation to build and render correctly.

The fixes here

1. Fix block quote shortcodes within case studies markdown files which were mangled by Crowdin
2. Untranslate some shortcode names and attributes which had accidentally been translated
3. Fix formatting of some figure shortcodes within case studies and the 2020 user survey.
4. Change the language name in the drop-down from the literally translated Inglés to Español.

cc @melissawm

Some of these things are just due to Crowdin mangling the shortcodes, but I think we should also include in the translation documentation some guidelines for translating content within and around shortcodes, (or find a way to make it so Crowdin doesn't suggest users translate things which we know shouldn't be translated).