Use buttons for budgets actions

Using buttons for non-GET actions is better for accessibility, as
mentioned in commit 5311daadf.

app/assets/stylesheets/admin/budgets/actions.scss

@@ -6,7 +6,6 @@
   margin-top: -$gap;
 
   > * {
-    margin-bottom: 0;
     margin-top: $gap;
   }
 
@@ -14,6 +13,11 @@
     margin-top: $line-height;
   }
 
+  a,
+  button {
+    margin-bottom: 0;
+  }
+
   .preview-link {
     @include has-fa-icon(eye, regular);
     @include hollow-button;
@@ -24,4 +28,8 @@
       margin-#{$global-right}: $font-icon-margin;
     }
   }
+
+  .delete {
+    cursor: pointer;
+  }
 }