Adds sitemap.xml. Adds 'Help Translate' to translatable strings. Error messages and fn name cleanups. (#136)

* added a note about needing more than one language to be enabled to allow for a drop down

* Removing debug statements

* Add 'Help Translate' to translatable strings, improves error messages around missing translated strings, calls write-translations on some routes

* Adds sitemap.xml to live server and build. Versioning not supported. -- Also did some file name and module cache cleanups.

website/siteConfig.js

@@ -42,7 +42,6 @@ const siteConfig = {
     { doc: "installation", label: "Docs" },
     { page: "help", label: "Help" },
     { blog: true, label: "Blog" },
-    { languages: false },
     {
       href: "https://github.com/facebookexperimental/docusaurus",
       label: "GitHub"
@@ -61,6 +60,7 @@ const siteConfig = {
     secondaryColor: "#205C3B",
     prismColor: "rgba(46, 133, 85, 0.03)"
   },
+  translationRecruitingLink: "https://crowdin.com/project/docusaurus",
   copyright: "Copyright © " + new Date().getFullYear() + " Facebook Inc."
 };