[feature] [gen] name sub-app classes Foo::Bar::App

[postmodern]

In order to keep module namespaces, I think it would be useful to name the sub-app class ProjectName::AppName::App, where ProjectName is the module name for the whole project and AppName is the module name for the sub-app. This would make it easier to nest models or additional lib code in the sub-app namespace.

Example

$ padrino-gen project foo
$ cd foo/
$ padrino-gen app bar

Would produce a bar/app.rb file beginning with:

module Foo
  module Bar
    class App < Padrino::Application