RFR: Add an option to stream region sampling data to a file

[William Kemper]

This change adds two command line options to enable and configure a feature that has Shenandoah stream region sampling data to disk. These changes are complemented by changes in the [Shenandoah Visualizer](https://github.com/openjdk/shenandoah-visualizer) project to load and replay the logged region sampling data.

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Commit messages:
 - Whitespace fixes
 - Add a test that configured region sampling log file is created
 - Fixed Shenandoah log file path handling and file overwriting
 - Fixed copyrights and added default value to ShenandoahRegionSamplingFile option
 - Changed ShenandoahLogFileOutput to independent class and added copyrights
 - Added Shenandoah logging flags and Shenandoah log file formatting
 - Added logSnapshotsFile option in shenandoah_globals.hpp

Changes: https://git.openjdk.java.net/shenandoah/pull/82/files
 Webrev: https://webrevs.openjdk.java.net/?repo=shenandoah&pr=82&range=00
  Stats: 414 lines in 8 files changed: 394 ins; 15 del; 5 mod
  Patch: https://git.openjdk.java.net/shenandoah/pull/82.diff
  Fetch: git fetch https://git.openjdk.java.net/shenandoah pull/82/head:pull/82

PR: https://git.openjdk.java.net/shenandoah/pull/82