Adds get_pool_name_for_fs

This is a small function to pull data out of a filesystem path.
A working version of MovingAverage

As the lass comment says, this is meant to provide utility like uptime
where it gives the average of some statistic over different periods of
time. This allows you to see how actions you take now affect the
statistic, while still giving you a long view of things.
Use MovingAverage

This updates MonitorThread to use the MovingAverage class to print out
better stats for the tracked filesystem
Adds a movingaverage for transaction groups

This second moving average keeps track of the TXGs per second, a metric
that I want to start tracking.