Generate TimeSeries charts from AbstractActivityMonitor measurements

ClusterTimeSeriesReport - new class to hold TimeSeries data from
individual AbstractActivityMonitor objects.
TimeSeriesReportGenerator - new class to generate the chart from a
ClusterTimeSeriesReport object
LocalSystemMonitorChart - modified to use ClusterTimeSeriesReport
objects, instead of ClusterReport objects
AbstractActivityMonitor, CpuUsageMonitor, GcMonitor, MemoryUsageMonitor
- add support for getting the time when the first measurement in the
monitor was taken
LocalJmxMonitor - Synchronize the intervals when the
measurements are taken