Move to Symfony Flex

The structure changed completely.
Bundles are gone. Everything is flatten in the folder `src`.
I separated import & api controllers to avoid _pollution_ in the main controller folder.

config/routes/nelmio_api_doc.yaml

@@ -0,0 +1,12 @@
+# Expose your documentation as JSON swagger compliant
+app.swagger:
+    path: /api/doc.json
+    methods: GET
+    defaults: { _controller: nelmio_api_doc.controller.swagger }
+
+## Requires the Asset component and the Twig bundle
+## $ composer require twig asset
+#app.swagger_ui:
+#    path: /api/doc
+#    methods: GET
+#    defaults: { _controller: nelmio_api_doc.controller.swagger_ui }