Added file-based authentication

[NathanPERIER]

Added an option (-f) that loads the credentials from a json file. The file will be loaded if the arguments provided to the script aren't enough to authenticate the user. The json object can have any of the following four fields : email, password, token or cookie. For instance :

{
    "token": "oCyymtQ8RsSM1eAS"
}

It will make it easier to launch the script and more safe since the credentials won't be logged in the command line history. Also, if the script can't authenticate the user, it will now prompt for a username and password in the command line.