Add configurable title and subtitle v0.6.1

app/static/index.html

@@ -16,7 +16,7 @@
         <div class="brand-mark" aria-hidden="true">◫</div>
         <div>
           <h1 id="app-name">Photo Date Editor</h1>
-          <p>Local folder · in-place JPG, PNG, TIFF and HEIF metadata</p>
+          <p id="app-subtitle">Local folder · in-place JPG, PNG, TIFF and HEIF metadata</p>
         </div>
       </div>
       <div class="top-actions">