Bug 960252 - Split start page styles out of browser.css [r=sfoster]

--HG--
rename : browser/metro/base/content/browser.css => browser/metro/base/content/bindings.css
rename : browser/metro/theme/browser.css => browser/metro/theme/start.css
Bug 962212 (part 1) - Add missing removeObserver calls [r=ally]
Bug 962212 (part 2) - Basic private browsing in Metro, preffed off [r=ally]
Bug 964418 - Update mochiperf tests to use dom utils frame time recording and add some apzc tests. r=mbrubeck