Merge pull request #346 from wawe/option-comment-wording

Add an option to use common terms for comments.
Update translations (see #346 for context) (Fixes hhucn/adhocracy.hhu_theme#223)
Fix a German translation (Fixes hhucn/adhocracy.hhu_theme#264)
Make comment_wording variable affect additional translations.

Use 'Add argument' instead of 'reply' for comment_wording = False.
Add/Update German translations regarding replies.