Anticache value of app URL changes every time app is opened

The URL of the CMNG Angular app contains a anti-cache value. For example:

./angular/hippo-cm/index.html?parentExtIFramePanelId=Hippo.ChannelManager.ChannelEditor.Instance&antiCache=1465199954136

This number ensures the index.html file is not served from the browser cache. However, that value should (ideally) only change when index.html changes. Currently, it changes every time the app is opened (e.g. each time a user logs in). That means the file is never cached and re-fetched every time the app is opened, which puts additional load on the CMS the slows down the client.

That should be changed, for example by generating the value statically server-side so it only changes when the CMS is restarted.

While fixing this, we should also check the cache-busting logic of all other resources loaded by the Angular app. There should be cache-busting when needed, but resources should also also not bypass the cache completely.