ISIS UX Warning message when about to leave edit

#### Lets be more Informative

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 
Wouldn't it be simpler to make the checks in PHP and only load the JS if checks are fine? Looks a bit strange to me to pass PHP values into JavScript only to make checks on them during runtime. Same for the edit variable 3 lines above.
We could just not load the whole JavaScript if it's not needed.