rest: Get the stats age from the stats instead of doing two calls.
Added GOMAXPROCS to the server stats.
Need to actually add some stat quiescing stuff.

Also notice that if stats aren't running, we don't need to worry about
tracking whether we should stop it, so there's never any stat related
work to do if nobody's been looking.
Let's build out wait groups and then ignore them.
Five minute tasks should run less frequently than 15s
GetItem/SetItem no longer takes numPartitions param.

Since each bucket now remembers how many partitions is has via its
BucketSettings.NumPartitions, we no longer need to pass around
numPartitions as a parameter to GetItem() / SetItem().