Completely untie the backend from the frontend.

Build nginx and mariadb together with the app image.
Upgrade docker-compose configuration to 3 version.
Add cleanup step to the gitlab-ci.

docker/mariadb/Dockerfile

@@ -1,6 +0,0 @@
-FROM mariadb:10.2.11
-
-COPY custom.cnf /etc/mysql/conf.d/
-
-ENTRYPOINT ["docker-entrypoint.sh"]
-CMD ["mysqld"]

docker/mariadb/config.cnf

@@ -4,6 +4,7 @@ default-character-set = utf8mb4
 [mysqld]
 character-set-server = utf8mb4
 collation-server = utf8mb4_unicode_ci
+performance_schema = ON
 
 [client]
 default-character-set = utf8mb4