WIP on desired state sync
all references to SaveDesiredState now point to SyncDesiredState
removed Desired State TTL from config
refactored app store layout
fix analyzer test now that the keys have changed
turn cassandra integration tests back on
heavily refactored app fetching
store saves heartbeats, not instance heartbeats.  now to optimize
refactoring: now tests use a dea fixture to generate apps and heartbeats.  guarantees a consistent dea guid
actual state writes are optimized
minor naming change
store adapter delete now takes an array of keys
store can compact empty directories and expired dea summaries.  shredder defers to store.Compact
SaveHeartbeat => SyncHeartbeat (more semantically correct)
added metrics for desired state sync time
actual state listener tracks store usage