We were using `overflow: scroll` as a workaround with a problem we had
with the equalizer. But now we never need an extra vertical scroll bar,
and we only need an extra horizontal scroll bar on small screens.
Since the dashboard was using the class `admin-content` as well, we need
to apply to the dashboard the same changes we've done in the admin
section. I've extracted them into a mixin.
In some situations where JavaScript makes content disappear, the height
of the element calculated by foundation's equalizer isn't recalculated,
leaving blank space at the bottom of the page. I've seen cases where a
blank vertical space of 2000 pixels is on the page.
Using flexbox solves the problem, since CSS takes care of everything.
There's a flaky test creating a group for a budget which takes place
because toggling a form using jQuery sometimes results in the button not
being correctly clicked by Capybara.
Checking the page with `expect(page).to have_button 'Create group'`
before clicking the button doesn't solve the problem; it looks like in
those cases Capybara waits for AJAX requests but not for JavaScript
animations.
See also issue #2573.
Why:
* There is a data-equalizer attribute on the parent div, and a data-equalizer-watch on a sibiling div, and that breakes both the purpose of those values (Resize child elements of data-equalizer to have the same height. Ref: http://foundation.zurb.com/sites/docs/equalizer.html)
* That lack of attribute was breaking many specs consistently on localhost with phantomjs 2.1.1 on macos sierra (and ubuntu as reported by @amaia)
How:
* Just adding the missing 'data-equalizer-watch' attribute on the div child of the one using 'data-equalizer'
