Send more data to StackLead integration

Adding this to send more data and improve our coverage. Note that facade.userAgent() appears broken since options is bound to the Identify prototype not Facade prototype where the function is bound.

Also I considered adding some logic to prevent us identifying old users, but felt that would probably be best handled by consumers explicitly disabling us via .Identify('user_id', {StackLead:false, ...other traits...}). Am I right in assuming that would work? Also wasn't clear how often created() would be populated and if it would only be populated if the user explicitly set in the call.

```js
  if (payload.created && (Date.now() - payload.created > (1000 * 60 * 60 * 24))) {
    // skip if older than a day.
    return fn(null);
  }
```