flatten ResourceRecordSet.profiles()

Introduce `ResourceRecordSet.geo()` and `ResourceRecordSet.weighted()`, which deprecate ResourceRecordSet.profiles()

full rationale here:

https://groups.google.com/forum/#!topic/denominator-dev/rGHqWR3ENys

This change is to be applied to 3.7 as a bridge for removal of `ResourceRecordSet.profiles()` in 4.0