Lock the map when iterating
Record number of GCs
Log scollector stats every 30s
Force a GC when we're above 100MB
Remove the lock from sendBatch; log more

Before sendBatch would be guaranteed to not swarm our TSAF server with
many requests because it used the queue lock. Instead, let's just not
spawn it as a goroutine and leave the lock available for the methods
that actually modify the queue. This might help fixing the scollector
not sending bug we saw on the search servers.