Add more information in PluginManager
New option -l, --list displays list of existing plugins
New option -h, --help displays help
Deprecate options (
   -install = -i, --install
   -remove = -r, --remove
   -url = -u, --url
Catch ArraysOutOfBoundException when no arg given to install, remove or url 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)
Closes #3112.