The OutputHandler refactoring

[milo]

@jiripudil wrote a PhpStorm pluging for Tester. I would like to refactor the OutputHander to be able better provide information for TeamCity output (according to https://github.com/jiripudil/tester/tree/feature/teamcity-output).

It will be with BC breaks I guess. My idea is to create class like:

class TestRunHistory
    public $file;
    public $stdout;
    public $exitCode;
    public $result;
    ...
}

and pass it to OutputHandler interface. But I didn't even try that concept.

[milo]

Closing in favour of #370