Add support for FTP on admin-lists.js

[CodeRedDev]

Closes #330

This adds support for fetching adminlists via FTP.

This can be done by adding a source like the following to adminLists in config.json:

"adminLists": [
  {
    "type": "ftp",
    "ftp": {
        "host": "XXX.XX.XXX.XX",
        "port": 12345,
        "user": "username",
        "password": "p@ssw0rd"
    },
    "source": "/SquadGame/ServerConfig/Admins.cfg"
  }
]

[CodeRedDev]

As I am pretty new to Node JS and more professional JS projects I'm pretty sure some part of code does not follow best practices. Please give me some advice if you find some bad code here :)

Apart from code this seems to work pretty fine on my own Squad server.

[CodeRedDev]

Just realized that to complete this issue I would have to add the info above to the ReadMe.

Would appreciate to first have a code review before adding info to ReadMe that doesn't fit the final solution.