Test by default

Made a handful of changes to the way karma is setup. Will update the wiki with more detail but basic idea is:

`grunt` default task will build and test
`grunt server` build, run test server, watch for changes, build/test
`grunt test` just run the tests once
`grunt test:ci` run tests once in ci mode
`grunt test:server` start the test server
`grunt test:run` run tests once using server

Figure `grunt server` is what we want most people using for day-to-day development. Seems to be working pretty well, i was able to make changes to ember-app code/tests and see tests going red/green in background. Also the karma DEBUG mode is pretty cool.

karma grunt tasks are still there but hidden behind more generic `test` tasks, hopefully will make it easier if people want to swap karma for something else.

Test results now include coverage report. So `grunt` results look like:
![karma-coverage](https://f.cloud.github.com/assets/19201/773337/45bc02a2-e936-11e2-9750-57955f373d97.png)

and when running `grunt server` karma will output html coverage reports under tmp/public/coverage
![karma-coverage-html](https://f.cloud.github.com/assets/19201/773346/8e2f490e-e936-11e2-8bfd-dae5cb113842.png)