Using a checkbox wasn't very intuitive because checkboxes are
checked/unchecked when clicked on even if there's an error in the
request. Usually, when checkboxes appear on a form, they don't send any
information to the server unless we click a button to send the form.
So we're using a switch instead of a checkbox, like we did to
enable/disable phases in commit 46d8bc4f0.
Note that, since we've got two switches that match the default
`dom_id(record) .toggle-switch` selector, we need to find a way to
differentiate them. We're adding the `form_class` option for that.
Also note that we're now using a separate action and removing the
JavaScript in the `update` action which assumed that AJAX requests to
this action were always related to updating the `visible_to_valuators`
attribute.
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.
This way we'll be able to simplify it a little bit.
Note that the original partial didn't include the whole row and only
the cells. Since, most of the time, we include the whole row in
partials, we're slightly modifying the component.
