Implement functionality 'dashboard_ignore_changes'

Create a new panorama option called "dashboard_ignore_changes", allowing people to drag, resize and even close public dasbhoard panlets but changes are not saved. Ideal for bosses :-)
Remark: I did not patch _panorama_js_functions.tt , line 154 and newer
```
        [%+ IF readonly +%]
        if(TP.initialized) {
            return false;
        }
        [%+ END +%]
```
because those result in empty tabs for readonly dashboards, and thus also for the ignore_changes patch