Subprocess, Logging Tweaks

* Explicitly pass `os.environ` to `subprocess.check_output()`. Fixes
  bug in which the subprocess failed to inherit the package's environment,
  so `PluginUtils`' checks could find the Node binary but the new
  process could not.
* Add `print_diagnostics` setting, allowing the user to suppress verbose
  logging of JSBeautify's configuration.
Merge branch 'phyllisstein-master'
Use " instead of ' to stay consistent with the rest of the file