(bug 24298) Make dropdown menus in Vector more accessible by expanding and collapsing...

(bug 24298) Make dropdown menus in Vector more accessible by expanding and collapsing them when the hidden link behind the dropdown arrow receives a click event (triggered by an enter or space bar key press in the typical use case) and changing the appearance of the arrow when the hidden link behind it is focused. Patch by Jan Paul Posma
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M    phase3/skins/Vector.php
M    phase3/skins/vector/images/arrow-down-icon.png
M    phase3/skins/vector/screen.css
AM   phase3/skins/vector/vector.js
M    phase3/resources/Resources.php