Prod packaging v1 (#23)

* Sets media directory for prod

* Improved logging; Added docker files for prod

* Improved fetching SECRET_KEY_BASE for selfhosted instances

docker-compose.ci.yml

@@ -1,7 +1,9 @@
 version: '3'
 services:
   phx:
-    build: .
+    build:
+      context: .
+      dockerfile: dev.Dockerfile
     volumes:
       - '.:/app'
     ports: