Hide completed and failed

[hiqua]

Not sure how much you'll like the first commit. I can split this PR in two if that requires more discussion. The behavior change itself is relatively small (see second commit).

See #1049.

[iSoron]

Thank you for the PR, @hiqua.

1. The refactoring is fine, but could you please submit it as a separate PR?
2. Could you please add some tests for isFailedToday?
3. If question marks are enabled, we also need to modify the menu message from "Hide completed" to "Hide entered" or something similar.

[hiqua]

1. done
2. should I have different tests for isFailed or should I just insert assertions in the isCompleted tests that are already in the codebase? I was copy-pasting the tests until I realized you might prefer that I just add assertions inside the existing tests.
3. ok trying to do that

Edit:
a. we also need to think about any possible interaction with the skip option
b. just because the unknown option is disabled, does not mean that the last tick is not a "no", since it could have been ticked while the option was active and before the user deactivated it again. So maybe sticking to one phrasing would be better, but we can talk about this once I have some preliminary version working.

[iSoron]

should I have different tests for isFailed or should I just insert assertions in the isCompleted tests that are already in the codebase?

Either way is fine.

just because the unknown option is disabled, does not mean that the last tick is not a "no", since it could have been ticked while the option was active and before the user deactivated it again.

I don't think this is a big issue. Most users will probably not keep switching back and forth between "hide/show question marks". I'd like to keep "hide completed" for users that have question marks disabled because I think it's much more clear.

[iSoron]

Looks good now, thanks!