Prevent additional test plans being unintentionally shown in test plan dropdowns

[howard-e]

#581 describes a case where unknown Test Plans were shown in the test plan management dropdown due to some test plan titles changing over time. #600 removes the duplicates but there still needs to be a way to prevent it from happening again.

Suggestion

With the inclusion of the TestPlan table in #620, it should make it easier to verify that only known test plans are listed and properly titled in that table when doing imports of new test plan versions.

#600 has been merged which includes a migration for the items no longer being shown in the dropdown.

A follow-up PR will follow which will prevent the chance of this happening in the future.

Originally posted by @howard-e in #581 (comment)