creating recurrence templates with due dates in the past allowed

#### To report a bug...

* What command(s) did you run?

`task add name due:2020-08-30 recurs:weekly`

as a typo instead of:

`task add name due:2022-08-30 recurs:weekly`

* What did you expect to happen?

Creation of a recurrence template going forward with one task appearing

* What actually happened?

A large number (>400) of tasks at weekly intervals from the past to present appeared. Thankfully this was easy to delete by deleting one task and selecting yes for "delete all pending recurrences".

#### To request a feature...

* Clearly describe the feature.

Produce a warning or a prompt on creating a recurrence template with due date in the past, or that would generate a large number of tasks.

* Clearly state the use case. We are only interested in use cases, do not waste time with implementation details or suggested syntax.

Prevent a clumsy user from accidentally borking their taskwarrrior :D