bug 936198 - update small Yahoo! icon, including on MetroFx, r=gavin

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extra : rebase_source : 770893767db1836b13e5cf4bd0904b402ce0d15b
bug 947275 - updated Bing branding for desktop and Metro, r=gavin

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extra : rebase_source : 375fe6e5cc5c7cc13326a35c1572c69dbec58bd1