Improve usability when user has unsaved form data, new dialog

Whenever the user leaves a modified (dirty) form that has not been submitted, OpenOLAT displays a dialog box to inform the user. This is implemented using a blocking

confirm

statement (part of JavaScript). The problem with confirm is that the buttons are defined by the browser (cancel and ok). The message therefore is a bit akward and when the user presses ok, the data ist lost.  

Specially in tests, users could think that pressing ok would magically send the answers to the server which leads to data loss. 

The dialog should be improved with a better information and more intuitive button labelling. 

Note that is it not possible to remove the old-style dialog entirely. There are still settings where a blocking dialog is required, however there are not many of this situations. The QTI1 system is an example: this will still show the old-style message. In most other situations, including QTI2, the new message will appear.