Post follow and updates notifications V1 (#111)

* It is now possible to follow a post in order to receive updates about it
* Notifications are now sent when updates are published
* Post status changes are now tracked
* Update sidebar now shows the post status history
* Mark a comment as a post update using the comment form
* ... more ...

docker-compose.yml

@@ -6,7 +6,7 @@ services:
       - POSTGRES_USER
       - POSTGRES_PASSWORD
     volumes:
-      - ./tmp/db:/var/lib/postgresql/data
+      - dbdata:/var/lib/postgresql/data
   web:
     build:
       context: .
@@ -26,4 +26,7 @@ services:
     ports:
       - "3000:3000"
     depends_on:
-      - db
+      - db
+    
+volumes:
+  dbdata: