We were rendering the whole sidebar again, which wasn't necessary since
most of it remains unchanged. This resulted in complicated code to pass
the necessary information to render the same map that was already
rendered. Furthermore, when users had been moving the map around or
zooming out, we were resetting the map to its default settings after
voting, which was potentially annoying.
This also fixes the wrong investments being displayed in the map after
voting; only the investments on the current page were displayed in this
case while the index displayed all of them.
We were rendering an individual ballot, and then rendering all ballots
(including the already rendered one). So we can skip the first part, as
pointed out by microweb10 in the comments of pull request 3036.
The `refresh_ballots` partial ignores the `investment` parameter
completely; instead, it iterates over the investments in the
`@investments` instance variable.
