Add recurring actions (and ignore them)
"EVERY day" recurring tasks
Choose when 'day' is considered to start

e.g., "EVERY day [9:00]" instead of "EVERY day".
Support sub-unit visible dates
Test: recur every N days
Test day-recurring actions with a range of days
Add weekly recurring actions
Actions which recur at specific times of the week
Avoid skipping intervals if recur is late

This prevents a critical and scary bug.  For example, without this fix, if you
pay your rent a day late, it won't remind you to pay the next month's rent at
all.
Tests correct day-boundary handling for due dates
Inherit ready-dates too