Very high CPU usage when it should be idle

[w-ensink]

After scanning a QR code the CPU usage goes up to 75-100%, even when back on the home screen doing nothing.
Before scanning a QR code for the first time, the app is at around 3% on the home screen, which is to be expected in debug mode.

I measured it in Xcode on a physical iOS device.

Issue seems to be this for loop: https://github.com/privacybydesign/irmago/blob/5ab0cec50ba16e921c1be95c6d7e414e4512d195/wait_status.go#L31-L33

It's caused by SSE, which is marked as experimental:
https://github.com/privacybydesign/irmago/blob/5ab0cec50ba16e921c1be95c6d7e414e4512d195/server/conf.go#L51-L52

Tried replicating by spinning up an irma server with

go run . server --allow-unsigned-callbacks --sse --url http://172.20.10.7:8088 --no-tls -v

And creating a session with

go run . session --pairing --issue irma-demo.MijnOverheid.ageLower=yes,yes,yes,no  -v --server http://172.20.10.7:8088

SSE seems to work this way, so it's not broken.