refactor(agent): Drop unused method GetOffer
refactor(agent): Track bids in a map
refactor(agent): Rename OfferResolved to DropOffer
refactor(agent): Clean up job state tracking

* Stash job state using TrackJob
* Track target state of all jobs scheduled locally
refactor(agent): Quit calling to the registry on Purge
fix(agent): Publish target states in Agent debug dump
fix(test): fix/simplify TestConflictsWith
refactor(agent): Simplify AgentState API

* Reduce the number of exported AgentState methods
* Move locking logic into AgentState
Merge pull request #362 from bcwaldon/agent-refactor

Various Agent refactoring