Description:

Installs a new AppExpress module.

Example:

`rails generate express_admin:install`

Creates a standard AppExpress module:
  app/assets/javascripts/express_awesome/admin/ajax_forms.js
  app/controllers/express_awesome/admin_controller.rb
  app/views/layouts/express_awesome/admin.html.et
  config/menu.yml
  lib/generators/express_awesome/install/install_generator.rb
  lib/generators/express_awesome/install/USAGE
  test/lib/generators/express_awesome/install/install_generator_test.rb

Adds an entry to config/routes.rb:
  `mount ExpressAwesome::Engine, at: ExpressAwesome::Engine.config.express_awesome_mount_point`

Adds a line to app/assets/javascripts/express_awesome/admin/application.js:
  `//= require express_admin`

Adds a line to app/assets/stylesheets/express_awesome/admin/application.css:
  `*= require express_admin`