Introduce support for a deploy-then-stabilise workflow with PendingCompo...

...nent.

PendingComponent is a decorator of Component that will:
 - always return INFO as it's status
 - report the status and value of the underlying component
 - log state changes in the underlying component (in a configurable way)

This supports the workflow of deploying a new component without causing unexpected warnings, until it can be declared "stable".