Support relative dates for "added" and "created" in filters & views

[jhqv]

After creating a view that was supposed to display documents added the past week, I quickly realized that the date chosen when creating the view is stored as an absolute date.

This means that creating a filter with the conditions "added: last 7 days" gives a filter that today and in the future will only return documents created after June 28th 2021. Saving a view like this is quite pointless since it won't give the expected results when viewed in the future.

Thus I suggest that the "last xxx" options in the "created" and "added" filters should be dynamic.