This commits removes the page 'Technical specs' and adds some technical info to the 'About' page.
The 'technical specs' folder and page were removed from the repo, from the navigation menu and
the footer (for all languages)

main:
 - [x] translated: de.yml - Status: peer-reviewed
 - [x] translated: lang\de\ - Status: peer-reviewed
 - [x] added: "de: Deutsch in other ymls"

resources:
 * untranslated: moneropedia - some terms added to match de.yml
 * untranslated: user guides
 * untranslated:  developer guides

Special thanks to ErCiccione and rodolfo912 as well as to rbrunner7