Add proposal name to vote links aria-label

This way blind screen reader users will know which proposal they're
supporting. In a list of proposals, context might not be clear when a
link saying "Support" or "Support this proposal" is announced, but a
link saying "Support Create a monthly transport ticket" is less
ambiguous.

Just like we did with investments in commit de436e33a, we're keeping the
title attribute because when visiting a proposal page, the connection
between the "Support" link and the proposal is not as clear as it is in
the proposals index page, so it might not be clear what you're
supporting.

config/locales/es/general.yml

@@ -408,6 +408,7 @@ es:
         one: 1 Comentario
         other: "%{count} Comentarios"
       support: Apoyar
+      support_label: "Apoyar %{proposal}"
       support_title: Apoyar esta propuesta
       supports:
         zero: Sin apoyos