--no-snippets flag for CLI

Now you are able to pass `--no-snippets` to the CLI and the formatters will not output the step definition snippets. So I added a `snippets` key to the `options` of the CLI configuration and set the value to `true` by default. This `options` object gets passed down to the summary formatter that supress the output of the snippets. I refactored the existing tests and added new specs and tests.

Hope this is helpful ;)