Translate into German

Edited also some Python files to get a complete translation.

Author:    Sven Claussner <sclaussner@src.gnome.org>
doc: add Sven to the credits

Signed-off-by: David Aguilar <davvid@gmail.com>
doc: add draft v1.8.4 release notes

Signed-off-by: David Aguilar <davvid@gmail.com>