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/variables.scss

@@ -0,0 +1,5 @@
+/* ==========================================================================
+   Variables
+   ========================================================================== */
+
+$blue-accent-color: #00acc1;