ISIS UX Warning message when about to leave edit 

#### Lets be more cautious

When editing an article, menu, category (anything singular), and press the back button the refresh or the close button on the browser, user most probably will loose any data without warning. This PR throws a standard browser window with custom message to inform him/her. Of course we are not forcing anything he/she can go ahead and close the window, but we did informed them 😃

#### Tests
Try opening any edit window (article, menu, category, banner, etc) in admin (isis default template).
Close the browser window
Refresh the browser window
Press the back batten on your browser

Please test in different browsers

#### How does it look like:
Safari
![screenshot 2014-10-17 15 34 29](https://cloud.githubusercontent.com/assets/3889375/4678857/42107510-55fb-11e4-813e-b52a37dc59ca.png)

Firefox
![screenshot 2014-10-17 15 44 44](https://cloud.githubusercontent.com/assets/3889375/4678867/6858900e-55fb-11e4-9e3e-f12d2609f6ce.png)

Chrome
![screenshot 2014-10-17 15 46 07](https://cloud.githubusercontent.com/assets/3889375/4678885/9732b31e-55fb-11e4-8e32-ccea89efa2c5.png)

Opera
![screenshot 2014-10-17 15 46 57](https://cloud.githubusercontent.com/assets/3889375/4678896/b05b6d4a-55fb-11e4-9576-2dee32dc5992.png)