Made QueueItem (formerly QueueEntry) a first class citizen

Now exposed in the Queue trait as enqueue/ack argument.
Queue statistics
Merge branch 'manu-feeder-data' into manu-rebuild-state

Conflicts:
	bwl-core/src/main/scala/com/wajam/bwl/queue/log/LogQueueFeeder.scala
	bwl-core/src/main/scala/com/wajam/bwl/queue/memory/MemoryQueue.scala
Merge branch 'master' into manu-rebuild-state
Update totalTaskCount as tasks are added and removed in LogQueue
Remove compilation warning
Finally get rid of the now useless QueueService
Killed the mutable.Set
Merge pull request #13 from wajam/manu-rebuild-state

Rebuild the persistent queue state when starting it by reading the entire transaction log