feat(archive_todo): add cron to archive todos

This is part 2 of habitrpg#3062. Part 1 MUST be merged first.
Part 1 pull request: habitrpg#3302
feat(archive_todo): update to archive todos

I thought this bit of code was in the other repo. So long as part 3 follows
close behind this, there shouldn't be an issue
Merge pull request #198 from jbutz/todo_archive_flag_cron

feat(archive_todo): add cron to archive todos