Consider: simplified update_vote

[stiffneckjim]

Consider:

 def update_vote(self, vote_type):
        vote_upwards = 1 if vote_type > 0 else -1
        same_direction = -1 if vote_upwards == self.track_vote else 1
        self.track_vote += vote_upwards * same_direction
        assert -1 <= self.track_vote <= 1
        self.save()

Originally posted by @sfkleach in #106 (comment)