Docker mix and match setup

Rewrite of the docker setup. Now uses fig to manage containers and container
linkage. The base is a block based mix and match, which will give you the
possibility to easily test all configurations.

docker/blocks/option_session_mysql/config

@@ -0,0 +1,3 @@
+[session]
+PROVIDER = mysql
+PROVIDER_CONFIG = ${SESSION_1_ENV_MYSQL_USER}:${SESSION_1_ENV_MYSQL_PASSWORD}@SESSION_1_PORT_3306_TCP_PROTO(${SESSION_1_PORT_3306_TCP_ADDR}:${SESSION_1_PORT_3306_TCP_PORT})/${SESSION_1_ENV_MYSQL_DATABASE}

docker/blocks/option_session_mysql/fig

@@ -0,0 +1,7 @@
+session:
+  image: mysql:latest
+  environment:
+    MYSQL_ROOT_PASSWORD: rootpass
+    MYSQL_DATABASE: gogs_session
+    MYSQL_USER: gogs
+    MYSQL_PASSWORD: password