Make the clear cache button work on desktop

Fixes https://github.com/vector-im/riot-web/issues/3597

src/BasePlatform.js

@@ -82,4 +82,12 @@ export default class BasePlatform {
     screenCaptureErrorString() {
         return "Not implemented";
     }
+
+    /**
+     * Restarts the application, without neccessarily reloading
+     * any application code
+     */
+    reload() {
+        throw new Error("reload not implemented!");
+    }
 }

src/components/structures/UserSettings.js

@@ -441,10 +441,10 @@ module.exports = React.createClass({
     },
 
     _onClearCacheClicked: function() {
+        if (!PlatformPeg.get()) return;
+
         MatrixClientPeg.get().store.deleteAllData().done(() => {
-            // forceReload=false since we don't really need new HTML/JS files
-            // we just need to restart the JS runtime.
-            window.location.reload(false);
+            PlatformPeg.get().reload();
         });
     },