Add support for Content Grouping

[marcorivm]

Content grouping allows us to create custom groupings for our site which can be used on many reports and allows for nice data aggregation which is difficult, at least from my limited experience, to achieve using custom dimensions or metrics.

See https://support.google.com/analytics/answer/2853423?hl=en for more info

[marcorivm]

I see that my personal js configs resulted on some unintended changes, like the import order or removing extra whitespace on the readme. If you think this is a problem I can revert these changes and make a clean commit

[ScreamZ]

Hello,

Thanks for your contribution :)

It might be a nice idea yeah, I see no issue with the idea of integrating this.
Don't worry much about linting configuration, I've made this library a while ago without really taking care of that. Maybe someday I should patch this and add a full lint little CI.

I see you're keeping pushing changes, lemme me know when it's ready for merge and I would deploy it

[marcorivm]

I noticed an error with the keys I had used, but should be good now. I deployed my version to production with one of our apps so I'll wait to collect data from today and let you know it's working.

Thanks for the quick answer and developing the package!

[marcorivm]

@ScreamZ I've been running this on production for almost two weeks now and its working correctly, it should be good for merging when you have some time.