Added masquerade dev module and disabled it by default.

- it allows to login as a given user by passing security check.
  - it must be used only during development!
  - disabled by default!
Updated the session auth module to make it easier to be reused.
  - masquerade module is based on the session auth module.

examples/demo/src/demo_cms_execution.e

@@ -91,6 +91,9 @@ feature -- CMS modules
 			a_setup.register_module (create {CMS_DEBUG_MODULE}.make)
 			a_setup.register_module (create {CMS_DEMO_MODULE}.make)
 
+				-- Dev
+			a_setup.register_module (create {MASQUERADE_AUTH_MODULE}.make)
+
 		end
 
 end