lb-add-copyright should keep the encoding declaration at the top of Python files

The encoding declaration for a python file must be at the top of the file (first or second line), see https://www.python.org/dev/peps/pep-0263/#defining-the-encoding

mentioned in merge request lhcb/Analysis!430 (merged)

created branch 14-save-python-encoding-declaration

mentioned in merge request !33 (merged)

closed via merge request !33 (merged)

mentioned in commit aa751c65