* feat(subscriber): award mystery items at cron
* fix(mystery): backfill skipped months
* fix(mystery): adjust subscriber text
* fix(mystery): correct moment logic
and remove irrelevant tests
* fix(mystery): build set one month in advance
* fix(mystery): don't add empty set to Time Travelers
* refactor(mystery): readability
* remove commented-out code for purging PMs - no longer needed
https://github.com/HabitRPG/habitica/issues/7940#issuecomment-406489506
* adjust comments
* move cron code when sleeping / resting back into main body of cron code
* rename tests to use consistent terminology for sleeping
* add tests for cron when user is sleeping
* move sleeping tests to same place as non-sleeping test
This matches how the code has sleeping and non-sleeping code mingled.
* replace a broken test with new tests
The deleted test wasn't working correctly. The check that the user's
health hadn't decreased would have worked even if the user wasn't
sleeping because the Daily had been marked completed.
The new tests test both no damage from incomplete Dailies and
that Dailies are reset.
* add tests for Perfect Day buff and rename existing tests for consistent terminology
* remove old test code
