title: Clear local Meteor Mongo collection on user logout
body: <p>I am starting to heavily use local minimongo collection</p>
  
  <pre><code>LocalItems = new Meteor.Collection null
  
  SomeOtherItems = new Meteor.Collection null
  </code></pre>
  
  <p>and i'd like to be able to empty all of these local collections when a user logs out;
  any suggestions?</p>