[Modified] The GitSpy now creates a different code files for each languages.

To sum up, the following files are created at each execution of the code by the student:
- exoFile : contains the code written by the student (extension is ".$language.code" where $language is java, py or scala)
- errorFile : contains the compilation error if there is one (extension is ".error")
- correctionFile = contains the correction of the exercise (extension is ".correction")
- instructionsFile = contains the instructions in html (extension is ".instructions")

I also removed the JGit messages from the PLM console (lines 41, 108, 113).