Ignore remote echos caused by this client

by sending each tag_ordering with a _storeId and ignoring accout data
that has a matching _storeId.

This will tend to become out of sync with the server over time if
requests continually fail, but subsequent successful requests will
rectify any differences.

src/actions/TagOrderActions.js

@@ -42,9 +42,14 @@ TagOrderActions.moveTag = function(matrixClient, tag, destinationIx) {
     tags = tags.filter((t) => t !== tag);
     tags = [...tags.slice(0, destinationIx), tag, ...tags.slice(destinationIx)];
 
+    const storeId = TagOrderStore.getStoreId();
+
     return asyncAction('TagOrderActions.moveTag', () => {
         Analytics.trackEvent('TagOrderActions', 'commitTagOrdering');
-        return matrixClient.setAccountData('im.vector.web.tag_ordering', {tags});
+        return matrixClient.setAccountData(
+            'im.vector.web.tag_ordering',
+            {tags, _storeId: storeId},
+        );
     }, () => {
         // For an optimistic update
         return {tags};