Fix fatal error in untouched tasks plugin

[APCBoston]

Fixes #926 . Fixes #912 .

Changes today in untouchedTasks.add_untouched_tag() to be a datetime.date instead of a datetime.datetime, making the comparison at line 114 (which was previously throwing an exception) valid.

[Neui]

Not fixed for me because new_time might be a datetime.datetime object depending how it was stored.
See #912 (comment) for more info.

Possible fix in my view:

The fix should either be using dt_by_accuracy(Accuracy.datetime) in untouchedTasks, or just always return an datetime in get_modified() (especially since fuzzy dates and different datetime formats aren't useful there).

Edit: You might also want to follow https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue to auto-close the issues with the correct syntax. You only need to write that in the PR description.

[APCBoston]

Thanks for those comments. It does seem like get_modified() should always return a single type. That said, for the sake of fixing the plugin before refactoring the core, I added a quick check to make sure new_time is always a core.Date or datetime.date, both of which can be validly compared. If it's a datetime.datetime, the datetime.datetime.date() method returns a datetime.date.

With this change I can't get it to fail with either type of return date from get_modified()

[diegogangl]

@APCBoston thanks for the patch! We're in the middle of a giant (and messy) port ATM. I'll wait until #894 is ready to land to check and merge this PR (and then fix the conflicts in the other pr).