Cannot create blackout date with returned / archived reservations overlapping [v5.5]

[orenyk]

Steps to recreate:

1. Create an archived or missed reservation
2. Attempt to create a hard blackout period that overlaps with said reservation

Expected: blackout can be created
Actual: blackout cannot be created

[orenyk]

Pretty simple fix, had to add the active scope when checking for conflicting due dates. I'll write some specs just to confirm (EDIT for master).

[orenyk]

Also, I just realized that we only check for conflicting due dates, but not conflicting start dates for future reservations... that doesn't make sense to me so I'll improve things.

[orenyk]

It also looks like we don't use the scope ends_on_days anywhere else, and we're using starts_on_days in a few places (but I'm not sure that we shouldn't really be using reserved_in_date_range instead, e.g. #1432 and reports), so I might open a separate issue to remove those if possible on master.