Rework claim interface

The current claim interface is clumsy and buggy. It's easier to redo it than to fix it.

Implement a wizard:

Entry page that dispatches dd/non-dds to the right next step
Claim for DDs where one picks the identifiers to claim
Claim email for DDs
Claim login for DDs
Claim fpr for DDs
Claim for non-DDs where one picks the identifiers to claim
Claim email for non-DDs
Claim fpr for non-DDs (has never been implemented so far)
Claim login for non-DDs (has never been implemented so far)

Edited May 05, 2020 by Enrico Zini

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