Upgrade to latest ember addon spec

Hey there, 

I wanted to try out your google api client but i was using a recent version of ember-cli and needed an up-to-date implementation, so here you go :tada: 

I have tried to change as little as i possibly can. The only thing that really changed in any meaningful way is the namespace of the internal files. I don't know how this will affect the plugin once it's being imported but i suppose it will be worth you testing this in one of your existing apps. 

All the tests are now passing and the new addon structure has a travis config so once/if you merge this PR we can setup travis to build the plugin. 

Also it's worth publishing this on npm too, I can do that for you if you like simply 2 command for me but let me know what you think. 

Cheers!