Support spoiling a ballot through API

[DJunge-w]

Need more details from EnhancedVoting team.

[DJunge-w]

A state filed [1, 2, 999] of a submitted ballot. Remember to reflect this state also in final encrypted ballot.

[DJunge-w]

An API for finalizing the ballot that decide whether spoil or cast a ballot. This method call returns the final encrypted ballot.

[DJunge-w]

This is a TODO after the first NPM package delivery.