Allow dropdown to act as a normal dropdown

Adding the .select class to .menu makes the dropdown act like a select.
Otherwise, it acts like a simple dropdown, keeping the "dropdown-button" value when clicking on a component of the dropdown.
It can be useful if you need a simple dropdown, but still use the version where it acts like a select.
@fabienb4 Thank you for pointing that out, in that case it's on us to convert everything to double quotes. Please make sure to use double quotes here, nonetheless.