More smooth workflow: use AJAX to check if field is uniqe

Now, module has this smooth flow:
- user type in for example node title
- user hit save
- module check if it is original - if not, display error message

Better workflow is to check originality of field before node is submitted using ajax:
- as soon as user leave field (focus off), ajax will check if field is uniqe.

You can take code inspiration from module Username originality AJAX check.

I found this in Username originality AJAX check issues: https://drupal.org/node/1399360 - Reproduce the same functionality as username check on fields