Add a aria-label to the mirador icon and i18n it

src/components/Branding.js

@@ -26,7 +26,7 @@ export class Branding extends Component {
             target="_blank"
             rel="noopener"
           >
-            <MiradorIcon titleAccess="About Project Mirador" fontSize="large" />
+            <MiradorIcon aria-label={t('aboutMirador')} titleAccess={t('aboutMirador')} fontSize="large" />
           </IconButton>
         </Typography>
       </div>

src/locales/en/translation.json

 {
   "translation": {
+    "aboutMirador": "About Project Mirador",
     "aboutThisItem": "About this item",
     "addedFromUrl": "(Added from URL)",
     "addManifestUrl": "Resource location",