**Note:** This is a small fix and should be easy to review.

Second fix for #3251.

In method `DataGroup.initializeData()`, if the passed `rawData` is bad for some reason,
it was possible to lose the subscriptions due to early return from the method.

This fix changes the order in the method so that the guard clauses execute *before* the
subscription is changed.

* First working version of eslint enabled with gulp

* Tryout of eslint with graph3d files

* Cleanup of gulp and eslint files.

* Completed test by linting graph3d

* Disable travis linting for now

* Remove global cmd param from .travis.yml

* Fix missing reference to Graph3D instance in DataGroup

Fix for #3251

A reference was missed in DataGroup.reload() during refactoring.
Rather than fix this method, it has been removed and the logic moved to `Graph3d`.
This makes for somewhat cleaner code.

* Fixes due to review

* First working version of new class DataGroup.

* Adjustments for review - done all points except last

* DRY distinct values, clean up sort code

* Added missing @param's to comments in DataGroup