Add LiipThemeBundle

Re-defined the config / user relation to be OneToOne bidirectionnal.
ConfigType is now a service so I can inject the list of available themes that are also used by LiipThemeBundle

Force sqlite for test
In case of people use a different driver in parameter.yml (yes I do :))

src/Wallabag/CoreBundle/Entity/Config.php

@@ -48,7 +48,7 @@ class Config
     private $language;
 
     /**
-     * @ORM\ManyToOne(targetEntity="User", inversedBy="config")
+     * @ORM\OneToOne(targetEntity="User", inversedBy="config")
      */
     private $user;