Added given_url in entry table

- Added index on entry table for given_url field
- Fix tests:

    The previous `bit.ly` url redirected to doc.wallabag but that url doesn't exist in the fixtures.
    I used our own internal "redirector" to create a redirect to an url which exist in the fixtures.

Also, updating current migration to use the new `WallabagMigration`.

src/Wallabag/CoreBundle/Repository/EntryRepository.php

@@ -368,6 +368,7 @@ class EntryRepository extends EntityRepository
     {
         $res = $this->createQueryBuilder('e')
             ->where('e.hashedUrl = :hashed_url')->setParameter('hashed_url', $hashedUrl)
+            // ->orWhere('e.givenUrl = :url')->setParameter('url', $url)
             ->andWhere('e.user = :user_id')->setParameter('user_id', $userId)
             ->getQuery()
             ->getResult();