Enable use of server side sign-in

As it is [documented](https://developers.google.com/api-client-library/javascript/reference/referencedocs?hl=hr#gapiauthauthorize), `gapi.auth.authorize` method can accept parameters that are not expected OAuth 2.0 params.

> If the key is not one of the expected OAuth 2.0 parameters (see below), it is added to the URI as a query parameter

This is necessary feature if someone wants to implement server side sign in. To achieve this, we need to set query param `access_type` to `offline`, and ask for `code` value to be retrieved. `code` value is needed on backed to do validation. That is why `response_type` has to be set to `code token id_token gsession`.

For more reference, look in [golang example](https://github.com/googleplus/gplus-quickstart-go/blob/master/index.html), where google native's 'g-signin' control is used. There property `access_type` is set to `offline`, which makes URL of google+ login popup contain query param  `response_type`=`code token id_token gsession`

Same functionality is achieved with this pull request.