Make auto-subscriptions wait until there is a logged in user

Nobody has claimed this yet.

This kind of a question / feature request.

Currently the package's [client code automatically subscribes to the roles](https://github.com/Meteor-Community-Packages/meteor-roles/blob/master/roles/client/subscriptions.js) and immediately causes data being loaded.

I would like to defer this step until my users are actually logged in reducing the initial data load when starting the app. I know this is just a tiny performance improvement but many of these small things add up in the end.

Proposed solution:

```javascript
Tracker.autorun(function () {
if (!Meteor.userId()) return
Roles.subscription = Meteor.subscribe('_roles')
})
```

I assume, that the information about user roles on the client makes no sense until there is not a logged in user (correct me if there is a usecase, that contradicts this assumption). Therefore this should not have any negative impact on current setups.

I could provide a PR for this

Start by reading roles/client/subscriptions.js, the file linked in the issue, and compare its current automatic subscription behavior with the proposed login-gated behavior. Verify that the roles subscription is deferred until a user is logged in and that existing package checks still pass.

Written by the indexing model from the issue text.