Add support for new-style rattail-demo install command

also use upstream menus where possible

rattail_demo/commands.py

@@ -44,3 +44,18 @@ class ImportSelf(commands.ImportSubcommand):
     name = 'import-self'
     description = __doc__.strip()
     handler_spec = 'rattail_demo.importing.local:FromRattailDemoToSelf'
+
+
+class Install(commands.InstallSubcommand):
+    """
+    Install the Rattail Demo app
+    """
+    name = 'install'
+    description = __doc__.strip()
+
+    # nb. these must be explicitly set b/c config is not available
+    # when running normally, e.g. `rattail-demo -n install`
+    app_title = "Rattail Demo"
+    app_package = 'rattail_demo'
+    app_eggname = 'rattail_demo'
+    app_pypiname = 'rattail-demo'