Update Ux/layout/Accordion.js

there was another layout bug in ST 2.1:
collapsing didn't hide the first list item; the generated html looks really different between ST 2.0.1 and 2.1; there are more elements and an ugly style !important attribute. I recognized a new css class "x-unsized", which causes the problem. Thats why I remove and add this class when collapsing and expanding. Not the best solution, but I have no time to find a better solution at the moment. Removing/adding the x-unsized class causes a flickering at least in Android 4.2, thats why I didn't use the css webkit-transition at the moment. Hope someone finds a better soltuion to fix this issue!