Merge branch 'stable-2.8'

* stable-2.8:
  Release notes for Gerrit 2.8.3
  Add clarification about commitWithin setting and reindex
  Update cookbook plugin revision
  Bump version to 2.8.3 in plugin API and archetypes
  Bump GERRIT_VERSION to 2.8.3

Conflicts:
	VERSION
	gerrit-plugin-archetype/pom.xml
	gerrit-plugin-gwt-archetype/pom.xml
	gerrit-plugin-gwtui/pom.xml
	gerrit-plugin-js-archetype/pom.xml

Change-Id: I29b59c9b2fe0967042bc67a7048d0b8374c54793