* toggleClass('class', undefined) behaves as if no second argument was
passed: a classic toggle
* toggleClass('class', !undefined) will only add the class if not
present, as the second argument is a boolean (!undefined is true)
This leads to an inconsistent state in the previous implementation of
multiple toggle methods (the`closed-menu` class was never toggled). We
now only use the not operator when the variable is not undefined.
Also, fix the toggle `closed-menu`/`open-menu` logic in dashboard.js,
where it was applied to the `a` instead of the `li`.
Simon Lejeune
b310a56c98