This is consistent to what we usually do. Also, we're applying the same
criteria mentioned in commit 72704d776:
> We're also making these actions idempotent, so sending many requests
> to the same action will get the same result, which wasn't the case
> with the `toggle` action. Although it's a low probability case, the
> `toggle` action could result in [selecting an investment] when trying
> to [deselect] it if someone else has [deselected it] it between the
> time the page loaded and the time the admin clicked on the
> "[Selected]" button.
Just like it happened with proposals, the button to select/deselect an
investment wasn't very intuitive; for example, it wasn't obvious that
pressing a button saying "selected" would deselect the investment.
So we're using a switch control, like we do to enable/disable features
since commit fabe97e50.
Note that we're making the text of the switch smaller than in other
places because the text in the investments table it is also smaller
(we're using `font-size: inherit` for that purpose). That made the
button look weird because we were using rems instead of ems for the
width of the button, so we're adjusting that as well.
Also note we're changing the width of the switch to `6em` instead of
`6.25em` (which would be 100px if 1em is 16px). We're doing so because
we used 100 for the minimum width because it's a round number, so
now we're using another round number.
We were checking it in the view, meaning that it was possible to toggle
the selection by sending a custom request even when the investment
wasn't feasible.
This way it'll be easier to change the link/button used to toggle the
selection.
Note that the conditions in the view seem to be different because we no
longer include the `selected?` condition when rendering the link/button.
However, an investment can only be selected if it's feasible and its
valuation is finished, so writing something like this would have been
redundant:
```ruby
can?(:toggle_selection, investment) &&
(selected? || investment.feasible? && investment.valuation_finished?)
```
The reason why the previous code was using the `selected?` condition was
to check whether to render the link/button to select or to deselect an
investment. We're now doing that in the Ruby part of the component.
