Go back to make_randomness, since the module initialization time is
noticeable otherwise.

Technical terminology:
 * EN: 1 vote = 1 signature + 1 ballot
 * FR: 1 vote = 1 émargement + 1 suffrages

 * move state to election_public_data

 - new module: Common
 - one table for all elections, and one table per election for votes
 - for now, forget about election_shortcut service
 - in production, the server only uses Ocsipersist
 - "<load>" directive in configuration file to load the Ocsipersist
   database from the filesystem at initialization time

 * max can be int or null
 * votes.json can be absent
 * incidentally, fix verify_partial_decryptions