Yannik ist dumm und hat änderungen vergessen zu pushen

See merge request !3

Fix security vulnerability of tool.

See merge request !2

- replace unsafe and uncomplete regex with validators.url to check if
  string is a valid url or not
- lessen docker container layer
- add python dependency validators
- fix pep8 issues in python code
- replace deprecated and unadvised os.system calls with subprocess
  calls

fixed typo

See merge request !1