More QA checks suggestions

[rubickcz]

• unsused imports (probably need to check all code, not only changes)
• invalid test method names (test_should_ is forbidden) (implemented in Add QA check for test method names #66)

[radimsuckr]

Test method naming check should be configurable (regex pattern or something like that).

[rubickcz]

@radimsuckr good point, however we just merged it hardcoded. I've discovered your comment late. But nevermind, we can implement this later.