The link to "See all investments" didn't have the `heading_id`
parameter, which resulted in the ballot information not being displayed
when in the voting phase.
We could modify the link to include the `heading_id` parameter, but IMHO
it's more robust to select the heading automatically when there's only
one heading. That way manually accessing the page without a `heading_id`
parameter will still work as if the heading had been selected.
caebaac1cc