Remove public env vars that cannot be set at build time

[krokosik]

Closes #609

The fix was to pass env vars during build stage in the Docker file. I realized I have been using client side env vars wrong, so I also:

• removed the cloud env var as it seems the cloud instance will never be updated
• removed Frankfurter currency filter, as they have recently added NBP currencies so are on par with our implementation
• rewired upload logic to use server side env var passed via server props