[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.
Not sure about the idea here. We do not tie Locations to the specific version, it is always on the published version.