Use tag to generate list of security related posts (en)

News posts tagged with "security" will be listed on the security page.
Add "security" tag to recent security related posts
Update security page to use generated list (de, it)
Update security page to use generated list (ja, id)
Update security page to use generated list (ko)

Also remove list of older and mostly not translated posts
(a link to the English page is already there).
Update security page to use generated list (es)

Also add a reference (in English) to the "en" page.
Update security page to use generated list (fr, pl, ru, vi, zh_cn, zh_tw)

Also remove list of older and mostly not translated posts,
and add a reference (in English) to the "en" page.
Mark security page as unmaintained (bg)

Also remove list of very old and not translated posts.
Display security posts on translation-status page in red
Merge pull request #663 from stomar/security-tag

Use tag to generate "known issues" list on security page