Internationalize template

config.toml

content/_index.en.md

content/blog/_index.en.md

content/gemeinschaft/_index.en.md

content/projekte/_index.en.md

templates/404.html

templates/base.html

templates/blog/meta_line.html

templates/blog/overview.html

templates/blog/post.html

templates/blog/section.html

templates/footer.html

templates/frontpage/blog.html

templates/frontpage/claim.html

templates/frontpage/events.html

templates/frontpage/projects.html

templates/menu.html

templates/menu/gemeinschaft.html

templates/menu/infos.html

templates/menu/projects.html