Add email to German share link description help.
Improve German translations.

This tries to improve the German translations in its context, making
them fit better in the layout, unifying different terms, fixing typos,
try to improve the readability and add some missing translations.
Merge pull request #917 from netzpirat/improve-german-translations

Improve german translations
FIX: Categories pill wasn't always being highlighted properly.
FIX: Hitting ESC while autocomplete is open shouldn't close the composer.
Show excerpts on Categories page
url for uncategorized category topic list is always /category/uncategorized
Display details about the search context in the placeholder
Merge remote-tracking branch 'upstream/master'