Feature: date filtering

[haszari]

All items have date info (e.g. imported, created, modified). The meaning is a bit fuzzy as these have not been consistently used, bulk-imports may have a fake/guessed date, and any date-looking hashtag (digits) may be interpreted as a date "mentioned".

The idea with list view is that items are shown most-recent-first. This breaks down because some tag-dates like #873458734587 push items to the top.

... ANYWAY it would be great to have date-range filtering, so can more easily focus on stuff from the last three months, a year, etc.