Upgrade to Meteor 0.8.3 (performance improvements).

Meteor release notes:
https://www.meteor.com/blog/2014/07/29/meteor-083
https://github.com/meteor/meteor/blob/release/0.8.3/History.md

* Used new `Template#autorun` method which automatically cleans up the
computation when the template is destroyed.

Change-Id: I4a0213ae84355701d88de268c0fc55bb36762fe9