[WIP] Rebind read only

The guts of the changes to support a read-only / hot-standby mode for management.

The design minimizes code changes and lends itself to being adapted for multiple masters looking after different entities.

For review only at this point; still I'd like to:

* Have a property determining whether default is `STANDBY` or `HOT_STANDBY`
* Failure on `HOT_STANDBY` moves to `FAILURE` mode
* Support `BrooklynObject` replacement on subsequent rebind (and unmanagement when items removed)
* Ensure `BrooklynObject` unmanagement and cleanup on demotion (this probably doesn't happen)
* Programmatic means of forcing transition from `FAILURE` to `STANDBY` or `HOT_STANDBY` (or `TERMINATED`) and from `MASTER` to `STANDBY`, `HOT_STANDBY`, or `TERMINATED`.
* Prevent activity for policies, feeds, enrichers, etc (possibly by promoting `suspend`/`resume` to `EntityAdjunct` and `AbstractEntityAdjunct` and in the latter checking the RO status of the entity; this won't catch everything but should catch most and make it easier to refactor those things which attempt a scheduled task inside `setEntity` ... that's not quite the answer, but in that direction I feel)

Subsequent to this we'll need some GUI/REST support to, at minimum, allow operators to access (after a warning probably) standby and failed servers, to display rebind problems, and to force a state change.

That will allow us to design a sensible `BrooklynCluster` with failover.
should it instead be `EntityTransientCopyInternal` ?

this is really about what methods we internally permit to be invoked on the RO copy.  we need to access its management support, i'm pretty sure.  we might get away with not exposing `setDisplayName()` as that should be done pretty close to construction time.