RFR: Add JFR parallel and concurrent events

[Zhengyu Gu]

The patch adds JFR parallel and concurrent events for Shenandoah.

It also reshuffles a few includes and moves 
ShenandoahWorkerTimingsTracker and ShenandoahTerminationTracker to 
separate files, to avoid recursive inclusion.


Webrev: 
http://cr.openjdk.java.net/~zgu/shenandoah/jfr_conc_par_events/webrev.00/index.html

Test:

   tier3_gc_shenandoah (fastdebug and release)

Thanks,

-Zhengyu