- don't update the index each time the panel is displayed (resource consuming when there are many repositories)
- start the RevisionIndexService when the MultipleGitRepositoryManagerImpl component gets loaded
  (Startable.start is only called when the whole plugin system starts, so the service wasn't started when updating the plugin)
- more logging
- don't override isUnique() and isInternal() as this is not needed
- unregister the RevisionIndexService before registering it, in case one was previously loaded