Exit confirmation in holiday management screen

[jaragunde]

It would be good to ask for user confirmation when leaving the holiday management screen, in case there are unsaved changes. It's specially interesting because there is no visual feedback on there being unsaved changes or not.

The tasks screen has the same feature and it can be reused in this case, we'd need to include this file and implement a function called isUnsaved():

https://github.com/Igalia/phpreport/blob/main/web/js/include/closeConfirmation.js