Added a command line mode

[anatolykopyl]

Needed this to create bash scripts that could chain commands together.
For example to execute photos command on multiple users listed in usernames.txt and put them in respective folders one would run a shell script like this:

while read username; do
  python3 main.py $username -c photos -o $username
done <usernames.txt

[Datalux]

Please can you update your PR with the latest commits in the development version?

[kappuccino]

@Datalux , can you merge this feature in the Dev branche ? this feature is a must have !

[kappuccino]

That was pretty fast !
thank you