Sepamail WebIDL syntax and algorithms

[rsolomakhin]

I suggest the following changes in in sepamail proposal:

1. The type of supportedNetworks should change from sequence to sequence<DOMString>.
2. The type of supportedTypes should change from sequence to sequence<BasicSepamailType>.
3. The name of SelectedNetwork should change to selectedNetwork.
4. The name of SelectedType should change to selectedType.

Also, please add some algorithms to process BasicSepamailRequest in the browser. At the very least, please specify what should happen if supportedNetworks or supportedTypes is an empty list. What should happen if supportedNetworks contains empty or duplicate strings. (I suggest throwing TypeError in all those cases.)

[marcoscaceres]

sepamailIdentifier should just be "id"

[ianbjacobs]

I believe Cyril has integrated comments:
https://w3c.github.io/webpayments/proposals/sepamail.html

(Cyril has asked Rouslan to verify.)

[rsolomakhin]

Looks good, thank you.

[ianbjacobs]

We have not worked on the sepamail proposal for a long time so closing this for now.