refactor(3): Move the functionality of the __init__ to a get_url() method which saves the result to a class property on the first call

build(gitlab#3): Add b5-init check whether skel is in a private repo or not, use ssh in case its a private repo

Introduce pylint

See merge request build/b5!6

fix: [useless-object-inheritance] Class inherits from object, can be safely removed from bases in python3

fix: [useless-object-inheritance] Classes 'StoredState' ans 'State' inherits from object, can be safely removed from bases in python3

fix: [useless-object-inheritance] Class 'StoredScriptSource' inherits from object, can be safely removed from bases in python3