Use SVG icons for the execute action buttons

This way we simplify the CSS and, in the case of the "check" icon, using
an SVG icon instead of an icon font offers several advantages, as
mentioned in commit 925f04e3f.

app/assets/stylesheets/dashboard.scss

@@ -142,25 +142,20 @@
   form {
     display: inline;
     vertical-align: top;
+
+    button {
+      font-size: 1.5em;
+    }
   }
 
-  .icon-check {
-    display: inline-block;
-    font-size: rem-calc(24);
-    vertical-align: top;
+  .checked-link {
+    @include has-fa-icon(check, solid);
+    color: $check;
   }
 
   .unchecked-link {
-    display: inline-block;
-  }
-
-  .unchecked {
-    border: 1px solid $border;
-    border-radius: rem-calc(4);
-    display: inline-block;
-    height: rem-calc(20);
-    margin-top: calc($line-height / 6);
-    width: rem-calc(20);
+    @include has-fa-icon(square, regular);
+    color: $border;
   }
 }
 

app/views/dashboard/_proposed_action.html.erb

@@ -6,7 +6,6 @@
         <span class="show-for-sr">
           <%= t("dashboard.recommended_actions.unexecute", name: proposed_action.title) %>
         </span>
-        <span class="icon-check"></span>
       <% end %>
     <% else %>
       <%= button_to execute_proposal_dashboard_action_path(proposal, proposed_action),
@@ -14,7 +13,6 @@
         <span class="show-for-sr">
           <%= t("dashboard.recommended_actions.execute", name: proposed_action.title) %>
         </span>
-        <span class="unchecked"></span>
       <% end %>
     <% end %>
     <div class="action-content">