Bug 1031018: Add a "Tools->Apps" menu item pointing to marketplace, r=MattN

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extra : rebase_source : f1ff6847c646dcba9d6001e79bb285ac35f27298
Bug 1031019: add "Apps" toolbar button that points to Marketplace, r=jared/Gijs

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extra : rebase_source : 32c104884c9a6116efd3911d8145b61b8aa5711b