Added data to Poll class and created Voter class

Started adding fields to Poll class.  Currently contains:
  - ID
  - Title
  - Description
  - List of voters
  - Encryption paramaters: group, g, and G

Also created a Voter class to represent Voters.

My plan is to have a unique instance of Voter for each voter in each poll (so
we won't reuse them between polls, even if we could).  I think that will
simplify our design.