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.

migrations/Version20170511115400.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace DoctrineMigrations;
+
+use App\Doctrine\WallabagMigration;
+use Doctrine\DBAL\Schema\Schema;
+
+/**
+ * Added `headers` field in entry table.
+ */
+class Version20170511115400 extends WallabagMigration
+{
+    public function up(Schema $schema): void
+    {
+        $entryTable = $schema->getTable($this->getTable('entry'));
+
+        $this->skipIf($entryTable->hasColumn('headers'), 'It seems that you already played this migration.');
+
+        $entryTable->addColumn('headers', 'text', [
+            'notnull' => false,
+        ]);
+    }
+
+    public function down(Schema $schema): void
+    {
+        $entryTable = $schema->getTable($this->getTable('entry'));
+
+        $this->skipIf(!$entryTable->hasColumn('headers'), 'It seems that you already played this migration.');
+
+        $entryTable->dropColumn('headers');
+    }
+}