SEO Improvements (#983)

* [site,seo][xs]: add custom _document with lang prop, add description to meta tags, make title larger

* [site,seo][xs]: add apple touch icon, add alt props to images

* [site,seo][xs]: add icon to default seo

* [site,seo][s]: implement next-sitemap

* [site,seo][s]: review page titles

* Rebuild package-lock.json files

* Regenerate package-lock

site/.gitignore

@@ -35,3 +35,8 @@ yarn-error.log*
 
 # markdowndb
 markdown.db
+
+# seo
+robots.txt
+sitemap-0.xml
+sitemap.xml