Install gettext in container to make makemessages work

Dockerfile

@@ -15,7 +15,8 @@ RUN apt-get update && apt-get install -y \
     libopenjpeg-dev \
     locales \
     cron \
-    postgresql-client
+    postgresql-client \
+    gettext
 
 # Add requirements and install them. We do this unnecessasy rebuilding.
 ADD requirements.txt /