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

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)
Merge pull request #9 from tim-group/pending-component

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