POC : Make Standard Triggers natively work like DataDriven Triggers

[jshaughn]

Do Not Merge until reviewed and dicussed. PR opened for review and to keep in sync with master.

I spent a few days investigating this somewhat major change to trigger semantics. In short it merges the data-driven group trigger feature into standard triggers. Put another way, it lets a single trigger handle data/events from N sources. The big difference is that it does it without using a backing group trigger. It's not totally seamless, there are some behavioral differences but I think the benefits justify the changes.

Here is a diagram of the approach: