[SPARK-8979] Add a PID based rate estimator

Based on #7600

/cc tdas

Author: Iulian Dragos <jaguarul@gmail.com>
Author: François Garillot <francois@garillot.net>

Closes #7648 from dragos/topic/streaming-bp/pid and squashes the following commits:

aa5b097 [Iulian Dragos] Add more comments, made all PID constant parameters positive, a couple more tests.
93b74f8 [Iulian Dragos] Better explanation of historicalError.
7975b0c [Iulian Dragos] Add configuration for PID.
26cfd78 [Iulian Dragos] A couple of variable renames.
d0bdf7c [Iulian Dragos] Update to latest version of the code, various style and name improvements.
d58b845 [François Garillot] [SPARK-8979][Streaming] Implements a PIDRateEstimator