Improve install command & add test

Also add fixtures for Config

InstallCommand now check if database, schema are here and ask the user what to do (keep or trash & re-create)

src/Wallabag/CoreBundle/DataFixtures/ORM/LoadEntryData.php

@@ -49,6 +49,6 @@ class LoadEntryData extends AbstractFixture implements OrderedFixtureInterface
      */
     public function getOrder()
     {
-        return 20;
+        return 30;
     }
 }