Disallowing Test Plans with Incomplete Tests

[aleenaloves]

Reference Issue: https://github.com/w3c/aria-at-app/issues/493

Per the working group, incomplete test plans cannot transition to the candidacy status. This PR is a fix for this issue.

I have ran all these test cases, but have also listed them here for people to double check and/or list if i missed anything.

Test Cases:

• Verify the test cases from the original issue no longer encounter the error
• Verify the behavior for an incomplete candidate test already existing

1. From another branch, transition an incomplete test plan to the candidate status
2. Migrate back to this branch, verify that the test navigator shows the correct icons for incomplete tests, the incomplete test also shows incomplete, and that a user cannot 'finish' this test.

• Verify the behavior for an incomplete test plan in review on the test queue page

1. Create an incomplete test plan
2. Set it's status to 'In Review'
3. Validate that you cannot transition it to 'candidate' and that it tells you why you cannot as well.

• Verify the styling in general
• Verify that nothing else is broken

1. General Test Queue Behavior
2. General Candidate Test Behavior

[ghost]

pending test fixes.

[ghost]

tests fixed.

[evmiguel]

Are we ok with the copy: Test plans with incomplete tests cannot be finished. These tests should have their candidate status removed.? @jugglinmike @howard-e

[ghost]

pending copy notes from isaac