Add an advanced census option

[elboletaire]

This option should have:

• A selector for the different census origins.
• Update the list of available census origins.
• Field for the census size.
• A field for the census root.
• A field for the census uri.
• A checkbox to tell whether the census is dynamic or not.

There is a new attribute of the process, which is maxVoters that is the old census size. By default, if it is not defined, it will be the same that the number of census participants.