Added mouse over titles for SB-Menu-titles..

..as discussed on #254 in @SUTJael's [comment](https://github.com/ampache/ampache/pull/254#issuecomment-45995138)
And made a final change on default.css to center icons on Sidebar top
I'm really sorry for double commit but you where faster with merging then me with
updating a second time^^

But all in all I think now its finished XD