[tutorial 021] A sub family

Inside a family, we can have variables or families.

The "type" for family "manual" became unecessary because container an other family, so it's not a variable.

In disabled attribute, it's better tu use relative path (we will see the reason in an other slide).

firefox/10-manual.yml

@@ -2,3 +2,7 @@
 manual:
   description: Manual proxy configuration
   type: family
+
+  http_proxy:
+    description: HTTP Proxy
+    type: family