Inaccessible by keyboard

[janlucaklees]

When focusing a selectboxit input using the tabulator, I can't open it using the space-bar or the enter key. For accessibility this is very bad. Users limited to keyboards can not use selectboxit inputs.

The drop-down should open, when the user hits enter or the space-bar on a focused selectboxit input. In addition the options should then be accessible using the arrow keys.