Splitted administration and normal web site interfaces.

This optimises a bit the routing map, and make cleaner separation.
Make the base url for admin pages customizable via `administration.base_path` variable in cms.ini
   note: could be /admin, /roc-admin, or ..
It is possible to have a specific theme for administration via the variable "administration.admin"

src/service/cms_administrable.e

@@ -0,0 +1,36 @@
+note
+	description: "Interface providing administration module."
+	date: "$Date$"
+	revision: "$Revision$"
+
+deferred class
+	CMS_ADMINISTRABLE
+
+feature -- Administration
+
+	module_administration: like administration
+			-- Associated administration module.
+		do
+			Result := internal_module_administration
+			if Result = Void then
+				Result := administration
+				internal_module_administration := Result
+			end
+		end
+
+feature {NONE} -- Implementation
+
+	internal_module_administration: detachable like module_administration
+			-- Cached version of `module_administration`.
+
+feature {NONE} -- Administration
+
+	administration: CMS_MODULE_ADMINISTRATION [CMS_MODULE]
+			-- Administration module.
+		deferred
+		end
+
+note
+	copyright: "2011-2017, Jocelyn Fiat, Javier Velilla, Eiffel Software and others"
+	license: "Eiffel Forum License v2 (see http://www.eiffel.com/licensing/forum.txt)"
+end