Rewrote Pocket Import

For the moment, we won't do a queue system, just a plain synchronous import.
We also use ContentProxy to grab content for each article from Pocket.
Error from Pocket are now logged using the logger.
The ImportInterface need to be simple and not related to oAuth (not all import will use that method).

src/Wallabag/ImportBundle/Resources/views/Pocket/index.html.twig

@@ -7,7 +7,7 @@
     <div class="col s12">
         <div class="card-panel settings">
             {% trans %}You can import your data from your Pocket account. You just have to click on the below button and authorize the application to connect to getpocket.com.{% endtrans %}
-            <form method="post" action="{{ path('pocket_auth') }}">
+            <form method="post" action="{{ path('import_pocket_auth') }}">
                 <input type="submit" value="Connect to Pocket and import data" />
             </form>
         </div>