support multiple private github repos in secret.conf

To support multiple private Github repos, secret.conf's auth_token can optionally be an object containing account : token pairs. 

"auth_token" : {"github_account1" : "personal_access_token1",
                        "github_account2" : "personal_access_token2"} 

Note that the names of the properties in the object are the github *account* name, not the repository names.  The function still honors the situation where auth_token is simply a string.