* add missing dependencies to be able to use docker
without these dependencies, the `docker-compose up` command is failing
- `rrdtool-dev` and `librrd` when building `rrdtool-0.1.15.tar.gz`
- `make` and `file` when building `gevent-1.5.0.tar.gz`
* disable secure cookies for being able to login when docker is used with runserver (there is no ssl)
* run develop command to avoid a hard failure after login when using the docker image (version check is performed but pkg_resources is not able to find modoboa distribution)
* polish multi stage docker build (adding missing dependencies for pip install and when running the application); use a virtual environment which is shared between the stages by using a base image and others will extend this
