Tidy up the dockerfile to preserve space

Dockerfile

@@ -1,7 +1,7 @@
 FROM cloudron/base:0.10.0
 MAINTAINER Johannes Zellner <support@cloudron.io>
 
-RUN mkdir -p /app/code
+RUN mkdir -p /app/code/taiga-back /app/code/taiga-front-dist
 WORKDIR /app/code
 
 RUN apt-get update && apt-get install -y \
@@ -10,27 +10,23 @@ RUN apt-get update && apt-get install -y \
     automake libtool libffi-dev curl git tmux gettext \
     python3 python3-pip python-dev python3-dev python-pip virtualenvwrapper \
     postgresql-9.5 postgresql-contrib-9.5 postgresql-server-dev-9.5 nginx \
-    libxml2-dev libxslt-dev
+    libxml2-dev libxslt-dev \
+    && rm -rf /var/cache/apt /var/lib/apt/lists /etc/ssh_host_*
 
 ## backend
-RUN mkdir /app/code/taiga-back
 RUN curl -L https://github.com/taigaio/taiga-back/archive/3.1.0.tar.gz | tar -xz -C /app/code/taiga-back --strip-components 1 -f -
 
 ## frontend
-RUN mkdir /app/code/taiga-front-dist
 RUN curl -L https://github.com/taigaio/taiga-front-dist/archive/3.1.0-stable.tar.gz | tar -xz -C /app/code/taiga-front-dist --strip-components 1 -f -
 
-RUN rm -rf /app/code/taiga-back/media && \
-    ln -s /app/data/media /app/code/taiga-back/media
+ADD build.sh nginx.conf conf.json conf_ldap.json local.py local_ldap.py start.sh /app/code/
 
 ## install all deps in a python virtual env
-ADD build.sh /app/code/build.sh
 RUN /app/code/build.sh
 
-RUN rm -rf /var/log/nginx && mkdir /run/nginx && ln -s /run/nginx /var/log/nginx
-RUN rm -f /app/code/taiga-back/settings/local.py && ln -s /run/local.py /app/code/taiga-back/settings/local.py
-RUN rm -f /app/code/taiga-front-dist/dist/conf.json && ln -s /run/conf.json /app/code/taiga-front-dist/dist/conf.json
-
-ADD nginx.conf conf.json conf_ldap.json local.py local_ldap.py start.sh /app/code/
+RUN rm -rf /app/code/taiga-back/media && ln -s /app/data/media /app/code/taiga-back/media && \
+    rm -rf /var/log/nginx && mkdir /run/nginx && ln -s /run/nginx /var/log/nginx && \
+    rm -f /app/code/taiga-back/settings/local.py && ln -s /run/local.py /app/code/taiga-back/settings/local.py && \
+    rm -f /app/code/taiga-front-dist/dist/conf.json && ln -s /run/conf.json /app/code/taiga-front-dist/dist/conf.json
 
 CMD [ "/app/code/start.sh" ]