Add more information in PluginManager

New option -list display list of existing plugins
Catch ArraysOutOfBoundException when no arg given to install or remove option
Add description on plugin name structure:
- elasticsearch/plugin/version for official elasticsearch plugins (download from download.elasticsearch.org)
- groupId/artifactId/version   for community plugins (download from maven central or oss sonatype)
- username/repository          for site plugins (download from github master)
PR for #3112.