feat($location): add support for state and title in pushState

This is a continuation of #3325, re-created per my e-mail thread with @IgorMinar.

Adds $location pushState & replaceState methods acting as proxies to history
pushState & replaceState methods. This allows using pushState to change state
and title as well as URL. Note that these methods are not compatible with
browsers not supporting the HTML5 History API, e.g. IE 9.
Hmm, actually, I need to be able to do `$location.pushState(state, '', 'the-same-url')` so I need to have a relaxed condition. Ideally I'd just skip the URL check here in HTML5 mode but `$browser` doesn't know about such a concept. I'll think about it.