Various fixes of warnings in tests

[Emkas]

• Fixed warnings in mocks - collective change for all warnings without changes in public interfaces
• Fixed warnings in component tests - as above
• HtmlResponseWriterTest: close writer - I know those are tests, but still, warnings easy to fix. I think this way is better than try-with-resources because any exception will break tests (and this is good)
• Remove unused code
• Remove empty UIComponent test overrides - they don't do anything. Tests are run anyway, because of the base class. This looks like generated code waiting to be filled.

[Emkas]

ping :-)

[arjantijms]

Thanks for the ping and the pr ;)