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
```ruby
gem_data = gem =~ /\.gem$/ and File.file?(gem) ? Gem::Package.new(gem).spec : Gem::Specification.find_by_name(gem)
```