1944 Internationalizes landing and audit pages

[misaugstad]

Resolves #1944

This PR adds the structure to internationalize the landing and audit pages. It also adds Spanish language translations for most of the landing page, and a good portion of the audit page (crucially, the entire tutorial). These translations were graciously provided by Edgar (@gari01234) from Liga Peatonal.

Things we are missing:

• Only the landing and audit pages have been translated. So we are missing translations for the validation page (and the whole rest of the website).
• There is still a decent amount to be translated in the audit interface. Anything that doesn't appear in the tutorial still needs to be translated.
• Missing internationalization of the dates/times.
• Any text that was in an image hasn't been translated yet. We need to create new images for each language, or ideally overlay the text onto the images.
• There are just a few small things that were missed, especially on the landing page.

I think it's best to get this code out on the test servers now instead of trying to fix all of the small translations we are missing.

Here's what the pages look like!

[gari01234]

Things we are missing:

• Only the landing and audit pages have been translated. So we are missing translations for the validation page (and the whole rest of the website).
  I can start with these translations.

• There is still a decent amount to be translated in the audit interface. Anything that doesn't appear in the tutorial still needs to be translated.
  Is there any easy way I can find what needs to be translated?

• There are just a few small things that were missed, especially on the landing page.
  This is regarding translations?

[misaugstad]

@gari01234 I can be more proactive about getting a list of translations for you so you don't have to search around the interface. Hopefully sometime tomorrow I can get you an initial list of things to translate!