Keep url in exists endpoint

- Add migration
- Use md5 instead of sha512 (we don't need security here, just a hash)
- Update tests

app/DoctrineMigrations/Version20190401105353.php

@@ -0,0 +1,44 @@
+<?php
+
+namespace Application\Migrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Wallabag\CoreBundle\Doctrine\WallabagMigration;
+
+/**
+ * Add hashed_url in entry.
+ */
+class Version20190401105353 extends WallabagMigration
+{
+    /**
+     * @param Schema $schema
+     */
+    public function up(Schema $schema)
+    {
+        $entryTable = $schema->getTable($this->getTable('entry'));
+
+        $this->skipIf($entryTable->hasColumn('hashed_url'), 'It seems that you already played this migration.');
+
+        $entryTable->addColumn('hashed_url', 'text', [
+            'length' => 32,
+            'notnull' => false,
+        ]);
+
+        // sqlite doesn't have the MD5 function by default
+        if ('sqlite' !== $this->connection->getDatabasePlatform()->getName()) {
+            $this->addSql('UPDATE ' . $this->getTable('entry') . ' SET hashed_url = MD5(url)');
+        }
+    }
+
+    /**
+     * @param Schema $schema
+     */
+    public function down(Schema $schema)
+    {
+        $entryTable = $schema->getTable($this->getTable('entry'));
+
+        $this->skipIf(!$entryTable->hasColumn('hashed_url'), 'It seems that you already played this migration.');
+
+        $entryTable->dropColumn('hashed_url');
+    }
+}