On this page, the user can choose how credential will be managed, and
the authentication scheme. The goal is to simplify the workflow
afterwards.

We keep it around for server upgrades...

It was redundant with ELECTION_DATA.

This field was most of the time set to None. The only non-None usage was
not really needed.

 - introduce sub-module D with signature WEB_ELECTION_DATA
 - Web_templates functions now take WEB_ELECTION_DATA

Rationale: sub-modules E and B are seldom used, eventually we want to
create them on demand and get rid of election_table. D can be directly
created from database. Long-term goal: get rid of register_election
and election_table, and have a constant server startup time.