add header font size vars to customizer page

customize.html

@@ -380,6 +380,22 @@ base_url: "../"
         <input type="text" class="form-control" placeholder="1.428571429" data-var="@line-height-base">
         <p class="help-block">Used to calculate line-height throughout Bootstrap.</p>
       </div>
+      <div class="col-lg-6">
+        <label>@font-size-h1</label>
+        <input type="text" class="form-control" placeholder="floor(@font-size-base * 2.60)" data-var="@font-size-h1">
+        <label>@font-size-h2</label>
+        <input type="text" class="form-control" placeholder="floor(@font-size-base * 2.15)" data-var="@font-size-h2">
+        <label>@font-size-h3</label>
+        <input type="text" class="form-control" placeholder="ceil(@font-size-base * 1.70)" data-var="@font-size-h3">
+      </div>
+      <div class="col-lg-6">
+        <label>@font-size-h4</label>
+        <input type="text" class="form-control" placeholder="ceil(@font-size-base * 1.25)" data-var="@font-size-h4">
+        <label>@font-size-h5</label>
+        <input type="text" class="form-control" placeholder="@font-size-base" data-var="@font-size-h5">
+        <label>@font-size-h6</label>
+        <input type="text" class="form-control" placeholder="ceil(@font-size-base * 0.85)" data-var="@font-size-h6">
+      </div>
     </div>
 
     <h3>Code blocks</h3>