Introduce jquery formvalidator for com_users

#### Executive summary

This PR converts the form validation on com_users to use plain jquery (no mootools call on every form ).
Also NO MORE INLINE SCRIPTS!

#### Testing

1. Apply first PR #4888 (!important)
2. Apply this PR
3. In the admin area go to com_users and try to submit any form.

If no javascript errors are logged in your browser and the functionality remains the same your test is a pass in any other case please report the errors here

If it was  attached to an element event it should be done on document.ready but this is only a function that is used  by other elements (in this case is fired when a select box changes) so it's done when the DOM is ready. 

Also this code was executed like that originally so let's keep it. We have enough problems :D