Plugin manager

Plugin manager for the new plugin structure

 - Install
  - From Rubygems
    - Latest
     - Specific version
  - From gem file

 - List installed plugins
   - All
   - Specific name
   - Specific group

 - Uninstall a plugin

 - Update
   - Single plugin to latest version
   - Single plugin to specific version
   - All to latest version
Its to force it to nil in case they do set it for some reason. it could cause some weird behaviour otherwise.
The nil ensures that all gems ( plugins ) are considered before applying the group check on it.