ExternalProgram format to execute console programs at importing

Moved tests into a class to clean Program file.
* ExternalProgram.cs: Improved Import method:
Support variables (copy imported files to temp files)
Support to copy current data to temp file (ie: pass as an argument)
Support to specify output file

* FileManager.cs: Parameters from Game xml now in XElement type to
  support child nodes.

* SubtitleValidation.cs: Fixed bug with the path of some subtitle
  files.