Autosave package: localSaveService discards dates

[ArtiomTr]

Describe the bug
LocalSaveService in autosave package discards dates without any warning.

To Reproduce
Steps to reproduce the behaviour:

1. Create a form with a Date value
2. Add autosave with localSaveService on it.
3. Trigger load.
4. Form will throw an exception

Expected behaviour
Show a warning when trying to save a form which has Date values on it.

Additional context
Alternative, some library, which converts javascript object to string without losing object prototypes.