Make the clear cache button work on desktop

Implement reload in Platforms to support
https://github.com/matrix-org/matrix-react-sdk/pull/798

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

src/vector/platform/ElectronPlatform.js

@@ -139,4 +139,8 @@ export default class ElectronPlatform extends VectorBasePlatform {
     requestNotificationPermission() : Promise {
         return q('granted');
     }
+
+    reload() {
+        electron.remote.getCurrentWebContents().reload();
+    }
 }

src/vector/platform/WebPlatform.js

@@ -206,4 +206,10 @@ export default class WebPlatform extends VectorBasePlatform {
         }
         return null;
     }
+
+    reload() {
+        // forceReload=false since we don't really need new HTML/JS files
+        // we just need to restart the JS runtime.
+        window.location.reload(false);
+    }
 }