Add memory and CPU stats

[sv2]

[sv2]

System stats added:

"sys": { "rss": 59768832, "heapTotal": 36700160, "heapUsed": 20081776, "external": 5291923, "cpu": 0 },

top level sys stats provide current cpu and memory usage.
Timeline buckets now include sys stats as well, providing average cpu and memory usage on bucket's time interval.
Using data as provided by process.cpuUsage() and process.memoryUsage()
CPU % calculated based on
nodejs/node#6157