Renamed CMS_RESPONSE.add_..hook with subscribe_to_..._hook

Renamed CMS_RESPONSE.call_..hook  with invoke_..._hook
Renamed CMS_HOOK_VALUE_ALTER as CMS_HOOK_VALUE_TABLE_ALTER
Renamed CMS_HOOK_MENU_ALTER as CMS_HOOK_MENU_SYSTEM_ALTER
Added new CMS_HOOK_MENU_ALTER that acts on CMS_MENU object.

Cosmetic, comments.

cms/src/hooks/cms_hook_menu_system_alter.e

@@ -0,0 +1,21 @@
+note
+	description: "[
+			Hook providing a way to alter the CMS menu system.
+		]"
+	date: "$Date$"
+
+deferred class
+	CMS_HOOK_MENU_SYSTEM_ALTER
+
+inherit
+	CMS_HOOK
+
+feature -- Hook
+
+	menu_system_alter (a_menu_system: CMS_MENU_SYSTEM; a_response: CMS_RESPONSE)
+			-- Hook execution on collection of menu contained by `a_menu_system'
+			-- for related response `a_response'.
+		deferred
+		end
+
+end