Move the button so that it appears in the Winners tab of the
budget_investments index.
When the budget is in "Balloting projects", "Reviewing Ballots"
or "Finished budget" phases, the button will appear as a button
(clickable). If there are no winners calculated yet, the text
will be "Calculate winner investments"; if there are, the text
will be "Recalculate winner investments".
If the budget is in another phase, the button will be
disabled and a message will appear: 'The budget has to stay on
phase "Balloting projects", "Reviewing Ballots" or
"Finished budget" in order to calculate winners projects'