Add sample 'hello world' app and enabled_apps config variable.

apps/hello/app.rc

@@ -0,0 +1,12 @@
+fn hello_test {
+    ~ $req_path /hello
+}
+
+fn hello_setup {
+    app_body_handler = 'hello_body'
+    pageTitle='Hi title!'
+}
+
+fn hello_body {
+    echo 'Hello world!'
+}