[DropDownMenu] Add option to make dropdowns editable

[kluplau]

Nice work.

I have two issues tho, on the dropdown.

• When you double-click on the dropdown on Chrome on Mac, then it breaks the dropdown.
• Further more, it should be possible to click twice, and then type in letters on the keyboard to navigate the dropdown.

[plus-]

double clicking breaks it on Chrome/win7 too. This is better described in #43

[hai-cea]

The double click problem has been fixed from #43. Changing this issue add an option for an editable drop down. See image for reference.