add support for group and identify

[sperand-io]

thought this would be a cool custom/versioned integration release example, as G asked for this today @ 2PM and we can be live 2 hours later with an integration update affecting only interested customers (in this case, us!)

Changes:

If there are any mapped traits in group or identify payloads, makes hit with:

event action = 'identify'|'group'
event label = 'identify'|'group'
event category = 'user'
uid = 'userId'
cm$ = 'value'
cd$ = 'value'

... and the other baseline payload params. I validated that the hits pass validation with the GA Debug endpoint.

[sperand-io]

@amillet89 @thehydroimpulse

[sperand-io]

that said, we should talk to some customers and see if we should ship this (behind an option flag perhaps?) to everyone