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.
What about scripts (with no `.py` ending)? Enforcing a license there seems even more valuable to me, as these are usually the things that users see.