Some further tidies in wake of latest location leak

A few things following on from #229 , mainly in `LocationRegistry` API.  @neykov can you cast your eye over this please?
`null` for `manage` meant to rely on the flags, and manage if no flags; that's the default used in most places.  but fair enough to say `true` means leave unset (so rely on flags).  will change to `boolean`.