[Refactor] Unify the invocation of external processes and properly grab STDOUT and STDERR

[GerHobbelt]

Been looking at the code for a while now and there's plenty places where external applications are executed, each with its own special flavor of code (probably as experience grows and history has its way 😄).

Meanwhile I'm pondering 🤔 that this is nice to have for running JavaScript scripts and bash/powershell scripts on PDFs and metadata so that I could integrate the nice parts of my old reverse engineering and work around Qiqqa project and PDF-in-the-Wild nastinesses.

Anyway, today the bubble popped and this issue got filed. Case in point:

QiqqaOCR generates a fault and the logging cannot dump its report properly because STDERR just so happens to have gone the way of the Dodo. Sigh. And if it just had said in there: "Exception bla bla, no words to write ladidah" it would have saved me some time.

Debugging QiqqaOCR with the same GROUP parameters gives:

The thread 0x264 has exited with code 0 (0x0).
Exception thrown: 'System.Exception' in QiqqaOCR.exe
We have no wordlist to write!

🎉 tada! 🎉

[GerHobbelt]

Standard idiom now looks something like this:

using (Process process = ProcessSpawning.SpawnChildProcess(ConfigurationManager.Instance.Program7ZIP, process_parameters, ProcessPriorityClass.Normal))
{
  using (ProcessOutputReader process_output_reader = new ProcessOutputReader(process))
  {
    process.WaitForExit();

    Logging.Info("XULRunner installer:\n{0}", process_output_reader.GetOutputsDumpString());
  }
}

[GerHobbelt]

Done for now AFAIAC