Add tagged services for import

- list services in /import
- add url to import service
- ImportBundle routing are now prefixed by /import
- optimize flush in each import (flushing each 20 contents)
- improve design of each import
- add more tests

src/Wallabag/ImportBundle/Tests/Import/ImportChainTest.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace Wallabag\ImportBundle\Tests\Import;
+
+use Wallabag\ImportBundle\Import\ImportChain;
+
+class ImportChainTest extends \PHPUnit_Framework_TestCase
+{
+    public function testGetAll()
+    {
+        $import = $this->getMockBuilder('Wallabag\ImportBundle\Import\ImportInterface')
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $importChain = new ImportChain();
+        $importChain->addImport($import, 'alias');
+
+        $this->assertCount(1, $importChain->getAll());
+        $this->assertEquals($import, $importChain->getAll()['alias']);
+    }
+}