Add hide button in the user interface

The little menu with the hide notification link and block user link
has been added to each proposal notification.

JS for adding the fade efect has also been added.

config/locales/en/activerecord.yml

@@ -103,6 +103,9 @@ en:
       poll:
         one: "Poll"
         other: "Polls"
+      proposal_notification:
+        one: "Proposal notification"
+        other: "Proposal notifications"
     attributes:
       budget:
         name: "Name"

config/locales/es/activerecord.yml

@@ -103,6 +103,9 @@ es:
       poll:
         one: "Votación"
         other: "Votaciones"
+      proposal_notification:
+        one: "Notificación de propuesta"
+        other: "Notificaciones de propuestas"
     attributes:
       budget:
         name: "Nombre"