Added verbosity methods
minor #11274 Added verbosity methods to NullOutput (WouterJ)

This PR was merged into the 2.4 branch.

Discussion
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Added verbosity methods to NullOutput

These 4 methods were not added to the OutputInterface because of BC, but they should still be implemented in all classes which implement that interface. Otherwise we have to do nasty tricks...

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Commits
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0459249 Added verbosity methods