Docker support for production use

This commit adds a Docker infrastructure that is ready for production
use. It is meant to simplify the deployment of OSEM for everyone who
wants to host their own instances.

It includes many features like data persistence, automatic secret key
generation and persistence and automatic database initialization and
upgrading. This should make updating the Docker container as easy as
possible.

docker-compose.env.example

@@ -0,0 +1,38 @@
+## database related variables ##
+
+# variables prefixed with MYSQL_ are used by both database and web containers
+# variables prefixed with DATABASE_ are used exlusively by the web container
+
+MYSQL_DATABASE=osem
+MYSQL_USER=osem
+MYSQL_PASSWORD=changemeimmediately
+MYSQL_ROOT_PASSWORD=changemeevenmoreimmediately
+
+# the following settings should not be modified unless the database service
+# is renamed in docker-compose.yml or you plan to use an external database
+DATABASE_HOST=database
+DATABASE_PORT=3306
+
+
+## OSEM options ##
+# you can configure any option described in this document here instead of
+# having to create a .env file:
+# https://github.com/openSUSE/osem/blob/master/dotenv.example
+
+OSEM_NAME=Dockerized OSEM
+OSEM_HOSTNAME=http://localhost:9292
+OSEM_ERRBIT_HOST=localhost
+SECRET_KEY_BASE=changemechangemechangeme
+
+# these settings work for the MailHog server that is enabled by default in
+# docker-compose.yml
+# if you do not plan to use MailHog (you most likely don't want to), you need
+# to change these settings to use an external working mailserver, otherwise
+# your users are going to see the HTTP status 500 page
+# you should comment out or remove the mailhog service from docker-compose.yml,
+# too
+OSEM_EMAIL_ADDRESS=osem@mailhog
+OSEM_SMTP_ADDRESS=mailhog
+OSEM_SMTP_PORT=1025
+OSEM_SMTP_USERNAME=mailhog
+OSEM_SMTP_PASSWORD=mailhog