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This avoids having to restart ocsigenserver (and kill all sessions) at
each account creation.

We consider the contact empty if it is set to the default value.

Recent versions of Firefox now try to parse them and complain.

New tabs tend to be blocked by browsers nowadays.

Move election_params_of_string to Election, and decompose it into two
functions.

There was a confusion between atdgen-generated conversion functions
and our own. To avoid the confusion, call our own functions
raw_string_of_uuid and uuid_of_raw_string.