Merge branch 'stable-2.8'

* stable-2.8:
  Restore pom.xml for gerrit-plugin-gwtui
  Generate javadoc for gerrit-plugin-gwtui

The version in gerrit-plugin-gwtui/pom.xml is updated to 2.9-SNAPSHOT.

Change-Id: I580c1dff33609bfbff923f381c40326cb048b5f9