Added notion of "front" page.

Changed CMS_HOOK_BLOCK.get_block_view to accept only attached string for `a_block_id'.
Keep simple name in CMS_MENU_SYSTEM.
Module that implements a CMS_HOOK need now to redefine CMS_MODULE.register_hooks .
Added simple code for NODE_MODULE, in order to see something.
Added CMS_URL_UTILITIES that should be used to compute url for cms path such as "/foo/bar".
Implemented get_active in CMS_RESPONSE to update the "is_active" on each link.
Added NOT_IMPLEMENTED_ERROR_CMS_RESPONSE.
Implemented a few hooks in DEMO module, for testing.
Updated smarty template related code.

model/src/cms_local_link.e

@@ -98,6 +98,14 @@ feature -- Element change
 			children := lst
 		end
 
+feature -- Status change
+
+	set_is_active (b: BOOLEAN)
+			-- Set `is_active' to `b'.
+		do
+			is_active := b
+		end
+
 	set_expanded (b: like is_expanded)
 		do
 			if b then