Performance issue (cache-control: no-cache)

[Saiv46]

Symptom:

Nimiq Keyguard takes some time to load and display password prompt on every occurrence.

Reason:

Each of following URLs is being downloaded 5(!) times each time Nimiq Hub is opened:

https://keyguard.nimiq.com/assets/nimiq/worker.js
https://keyguard.nimiq.com/assets/nimiq/worker-wasm.js
https://keyguard.nimiq.com/assets/nimiq/worker-wasm.wasm

The problem is with Cache-Control: no-cache, must-revalidate, despite backend supporting (and sending) ETag and Last-modified headers, browsers will not even try to make conditional request to revalidate cache (as described for Request.cache).

Possible solutions:

1. Updating WasmHelper.js to use fetch() instead of XHR.
2. Fix Service Worker own caching to actually make it offline-capable.
3. Setting Cache-Control: max-age=60, must-revalidate should resolve this issue. CDN-Cache-Control could be used alongside.