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.

assets/themes/material/css/index.scss

@@ -0,0 +1,18 @@
+@import "variables";
+
+/* Style */
+@import "article";
+@import "cards";
+@import "entries";
+@import "filters";
+@import "layout";
+@import "nav";
+@import "sidenav";
+@import "various";
+@import "dark_theme";
+
+/* Tools */
+@import "fonts";
+@import "icons";
+@import "print";
+@import "media_queries";