backup: rename back backuplisting.js to backups.js

this was a transitional rename till I figured out how to split
it in backuptargets.js

src/routes/index.js

@@ -8,7 +8,7 @@ exports = module.exports = {
     appstore: require('./appstore.js'),
     archives: require('./archives.js'),
     auth: require('./auth.js'),
-    backupListing: require('./backuplisting.js'),
+    backups: require('./backups.js'),
     backupTargets: require('./backuptargets.js'),
     branding: require('./branding.js'),
     cloudron: require('./cloudron.js'),