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'
When there are no budgets we were seeing an exception in the budgets’
index
There are two parts to take into account here:
1) Making sure there is a current_budget present, otherwise we display
the “no budgets” message
2) The map helper is called from the controller, so we need to make
sure current_budget is present there too
Note: We could have added a bunch of `try` statements in the budgets’s
index, instead of using a conditional, however there are quite a few
`current_budget` calls so it seems more appropriate to use a conditional
