GPII-290: Return token(s) as JSON

var token = tokens.join(",") returns the list of tokens as comma-separated strings, while the message that no token is logged in is returned as JSON. 

One option is var token = JSON.stringify(tokens)

Another option is what I wrote ;-)

Some comments: 
* When I try to log in a token that requires software that is not installed locally (e.g. ReadWrite Gold), the system reports that no token is logged in. This seems strange. 
* When I fist log in sammy and then elaine (using URLs in the browser, and the software required for both is available locally), the system returns both tokens. I assume that is OK. 
* When I test this in a browser, the list of tokens is returned with the MIME type text/html, whereas the error message is returned as application/json.