Show "settings saved" message only, when all changes to configuration settings were saved

In #0001118 task we've added nice message, that is shown on configuration page when all settings were successfully saved.

However after using it a bit on my projects I've discovered, that message is shown if at least one of system settings, displayed on a page, was saved successfully.
Also on "Configuration -> Website -> Advanced" page, which is quite long, it's hard to see error in a setting value is is at the bottom of a page.

I'm proposing to:

1. display "Saved" message only when ALL system settings were saved without validation errors
2. scroll window/frame to first error on a page