Allow to cancel modal hiding in `hide` event handler.

Created by: romanych

In case you show form in modal you might want to add confirmation on close button click. It is very easy to do:

$('#myModal').on('hide', function() {
    if (!saveButtonClicked && hasChanges) {
        return false;
    }
});

or

$('#myModal').on('hide', function(e) {
    if (!saveButtonClicked && hasChanges) {
        e.preventDefault();
    }
});