Introduce jsdoc examples to insight.DataSet

Examples show the data along with the differentiation between
one-to-one and many-to-one groupings.
Improve insight.DataSet.group example

In response to PR feedback. Change should hopefully provide additional
clarification as to how group is used.
Updated DataSet.group @example
Merge pull request #1 from niksoper/feature/dataset-group-doc-example

Updated DataSet.group @example
Merge pull request #254 from matthewdunsdon/feature/dataset-group-doc-example

Introduce jsdoc examples to insight.DataSet.group
Fix missing package dependency

- Missing ```grunt-zip```
- Packages reordered by ```npm```.
Merge pull request #257 from matthewdunsdon/fix-package-json

Fix missing package dependency