[Spec] Location drafts

Discussion on spec for location drafts in SPI.

API: This is just a first step, basically introducing support for Location drafts Content on version 1, to fix issue with preview.

SPI: Further steps will be needed now/later like exposing a method on LocationHandler to change status, which will be more optimal then setting it on Location update struct. PS: PR removes $rootLocationId as it can easily be done in API as shown here.
It should be sufficient, this is what we already have in ContentHandler, and I would actually prefer it that way.