Dropdown: open the menu on top

[veej]

requirements

In some cases it could be helpful to have the dropdown menu open at the top instead of bottom (i.e. when dropdown is near the bottom of the page and the menu will overflow the screen)

specs

• add a new prop menuPosition with possible values: ['top', 'bottom']
• add a new css class when menuPosition: top, defining the style as described here: How do I make the dropdown open at the top instead of bottom? JedWatson/react-select#403

misc

{optional: other useful info}