Preparation for Issue #90 and license checking

This pull request contains a simple script to check that all licenses within the project look the same. I would like to discuss the script and create a external plugin for license / text file header checking afterwards.

All project python source files (including tests, except build.py and check_licenses.py) have the same file encoding comment and license header now.

I created simple tests for the plugins PyFix, PyMetrics, PyLint, Pep8.
Did you have an idea, when you want to do the replacing? When packaging (e.G. on the sdist only?) Or would it be a one-time thing where you tell PyBuilder to put the license into every file, correcting and adding as required?

I think it's important that the license is in each file all the time (even in the VCS repo) because people who want to contribute need to know how the code is licensed. So IMHO that excludes a step during packaging where the license is "inserted".