Generate tokens for all users logging in

For closed polls, the users should have a token already.
For open polls, it will check if they already have a token, and generate
one if not.
Hook up front-end for token login

Logging in to an open poll now generates a token and stores it in the
local storage, so even switching between google and facebook logins with
different names still have the same vote set returned.
Enforce tokens for voting

Requires that a vote contain a valid token for the poll