Improve add buttons

app/views/contests/show.html.slim

@@ -20,7 +20,7 @@
         h4
           = t("puzzles.plural").capitalize
           a.ms-3.btn.btn-primary href=new_contest_puzzle_path(@contest) style="margin-top: -3px"
-            = t("contests.show.add_puzzle")
+            | + #{t("helpers.buttons.add")}
     table.table.table-striped.table-hover
       thead
         tr
@@ -71,7 +71,7 @@
         h4
           = t("contestants.plural").capitalize
           a.ms-3.btn.btn-primary href=new_contest_contestant_path(@contest) style="margin-top: -3px"
-            = t("contests.show.add_participant")
+            | + #{t("helpers.buttons.add")}
     table.table.table-striped.table-hover
       thead
         tr