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fixes#4324
A multiline error message produces poor visualisation when used in the UI, while
there is no need for it to be multiline.
Remove runtime check when constructing FunctionExpression, in order to
support future built-in function. Exception will be thrown when
evaluating the expression to inform user about the error.
Dynamic property can be removed at any time, even during triggering of
onChanged() signal of the removing property. This patch introduced
static function Property::destroy() to make it safer by queueing any
removed property, and only deleting them when no onChanged() call is
active.
1 - Reports the error to the user in a popup.
2 - Names of the backups include the timstamp instead of a number. Names have more sense and the files can be sorted by names what is also the age order.
3 - Behaviors when changing configuration improved, the number of files present on the system was not reduced when reducing the number of backups or backups deactivated.