GA Event category should not be hardcoded to "Event"

[hraynaud]

HI first thanks for this great gem. I noticed that the google_universal support is only available on the master branch and not in any of the release branches. Is there an ETA when it will be officially released. Also, the event tracking api as implemented doesn't fully match google's spec.
https://developers.google.com/analytics/devguides/collection/analyticsjs/events

The current implementation hard codes the category as "Event", and doesn't support the last number parameter. I'm happy to provide a pull request with the desired enhancements but just wanted to check to make sure I didn't miss anything.

[sfsekaran]

Since we do support google_universal (yet), and the events are the true issue here, I'm editing the issue title.

Yes, the hardcoded category is a problem. What's your proposed solution? Also--how would your change affect the other tracking systems analytical supports?