Put a cachebuster in the names of CSS and JS files

This means that clients can do better caching of assets, as it will mean we are
no longer reliant on etags to ensure that clients get a fresh version.

We inhibit the cachebuster for `npm start`, so that we don't get millions of
copies of the bundles on dev boxes.

.gitignore

@@ -8,6 +8,7 @@
 /vector/bundle.*
 /vector/emojione/
 /vector/config.json
+/vector/index.html
 /vector/olm.*
 .DS_Store
 npm-debug.log