LB-1839: Merge master branch to devel

Fixed merging issues not signaled by git. ( due to the mixed CRLF vs LF)
Squashed 'plugins/embed/' changes from 02e244d..24db177

24db177 Merge pull request #199 from nistormihai/concurrency-fix
4418bac LB-1838: Incorrect timestamps on initial set of SEO/HTML posts
7bb3487 LB-1750: Update tageswoche theme
c178f32 Merge pull request #198 from nidzix/test
5cb7729 Ruhrnachrichten theme fix

git-subtree-dir: plugins/embed
git-subtree-split: 24db177fb47555e92c8f8f5587b016f476f34fa8
Merge commit '009bb83229232469ba5aab6282070ccfe15afad5' into devel-merge