Add style test for common file types
    
    Add linting script and run it against files with following extensions:
    - .jinja, .j2
    - .py
    - .sh
    - .sls
    - .yaml
    
    This is an effort to establish a common coding style and uniform
    datasets in our repository.
    
    Signed-off-by: Georg Pfuetzenreuter <mail@georg-pfuetzenreuter.net>