chore(karma): updates karma and add some neat test shortcut tasks

This updates the used karma-runner to latest `0.10.x` and corresponding Grunt task to `0.6.x`. Both are stable.

* This removes the "use firefox" override for tests in `package.json` which was actually only for Travis. Now, that behavior is set up in the configuration itself.
* Both karma configurations are upgraded to karma-runner 0.10
* Travis init-script enriches with `npm install -g karma-cli`
* Adds more convienient tasks
  * (not changed) `grunt test` runs the tests like before (unit and midway) in our standard browser (Chrome, or Firefox on Travis)
  * `grunt test-headless` runs the tests in a headless PhantomJS
  * `grunt test-firefox` runs the tests in a Firefox (should be available)
  * `grunt karma:debug-unit` respectively `grunt karma:debug-midway` starts the standard browser (Chrome), but wait for interaction by the user (i.e. for debugging in tests)