Update landing page of karma-runner.github.io

The videos and data on the landing page are quite outdated, it should be updated with new information.

Ideas, suggestions and help are very welcome.

cc @zzo if you have any case studies, use cases etc that you know of or ideas please post them :)

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### Inspiration:
- http://eslint.org/
- http://babeljs.io/

Start by locating the source for the karma-runner.github.io landing page and reviewing its current videos and data. Compare the page with the linked ESLint and Babel examples, then identify current information and case studies to include; done means the landing page content is updated and the outdated material is replaced.

Written by the indexing model from the issue text.