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.yml.example

@@ -0,0 +1,29 @@
+version: "2"
+
+services:
+  database:
+    image: mariadb:10.1
+    env_file: docker-compose.env
+    volumes:
+      - database:/var/lib/mysql
+
+  mailhog:
+    image: mailhog/mailhog:latest
+    ports:
+      - "127.0.0.1:8025:8025"
+
+  web:
+    build: .
+    env_file: docker-compose.env
+    depends_on:
+      - database
+      - mailhog
+    ports:
+      - "127.0.0.1:9292:9292"
+    volumes:
+      - "web:/data"
+
+# these named volumes are used to persist data
+volumes:
+  database:
+  web: