Added an example of store.pushPayload

The models and data are indicative of what I'm using in my app. I noticed
a significant slowdown on Android (my target platform) for adding data to
the store when I upgraded from Ember 1.7 and Ember Data beta 9 to
Ember 1.8 and Ember Data beta 11 - this should allow other people to
reproduce the slowdown...
Added a total time row to the bottom of the table
Removed computed properties to make sure they aren't effecting the
speed of pushing into the store...
Merge pull request #20 from vitch/feature/push-payload

Example of severe speed regression in ember-data
update