Revision controller needs some cleanup/organization

/area API
/kind cleanup

_Just revisited the revision controller after sometime. I figured I should write down my thoughts before I'm off on vacation starting now._

The revision controller is very fragile wrt. ordering of reconciling its child resources. Currently deployments are reconciled prior to pod autoscalers. Thus I've noticed:
1. Phases reading into the revision status may be reading stale data
- The deployment phase looks at the Active condition, then after the PodAutoscaler phase may update it
- `MakePA` looks at the revisions conditions to reconcile. Afterwards PA conditions are propagated to revision. Maybe this causes some churn?
1. Last `Mark*()` method wins - there's code in the PA phase to guard against overriding false conditions that it assumes the deployment phase has set
1. Re-ordering phases exposes assumptions:
- deployment phase (when deployment is not found) marks the revision as 'Deploying' - but the PA phase doesn't.
- test fixtures aren't accurate - ie. deployment was not ready when testing the steady state but still passed because of PA's ready state trumped all (see 2. above)