UX: Add a `span` to d-button so text can be hidden via CSS

app/assets/javascripts/discourse/templates/components/d-button.hbs

@@ -2,5 +2,8 @@
   {{fa-icon icon}}
 {{/if}}
 
-{{{translatedLabel}}}
+{{#if translatedLabel}}
+  <span class='d-button-label'>{{{translatedLabel}}}</span>
+{{/if}}
+
 {{yield}}

app/assets/javascripts/discourse/templates/navigation/categories.hbs

@@ -7,6 +7,11 @@
     {{categories-admin-dropdown}}
   {{/if}}
   {{#if canCreateTopic}}
-    <button id="create-topic" class='btn btn-default' {{action "createTopic"}}><i class='fa fa-plus'></i><span>{{i18n 'topic.create'}}</span></button>
+    {{d-button
+      id="create-topic"
+      action="createTopic"
+      icon="plus"
+      label="topic.create"
+    }}
   {{/if}}
 {{/d-section}}