GitLab

 - remove phony POST parameters
 - perform verification of submitted votes

 - 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

Use more abstract datatypes where possible:
 * Helios_datatypes_t.election
 * Uuidm.t