feat(config): Allow tests be to run in a new window instead of iframe

Some testing frameworks would need a new window and may not be able to run in an iframe. This pull request adds an option to open context.html in a new window instead of the iframe. For example, I am working on a (karma-telemetry)[http://github.com/axemclion/karma-telemetry] framework that uses telemetry to calculate rendering times of components. The times do not work in an iframe and need a new window. 

Based on a discussion in groups - https://groups.google.com/forum/#!topic/karma-users/6Ud2TvwhESc

Note that to test this, the browsers need to enable popups. For chrome, this would be 

```
 customLaunchers: {
        'ChromeNew' : {
            base: 'Chrome',
            flags: '--disable-popup-blocking'
        }
    },

```