feat($location): add ability to opt-out of <base/> tag requirement in html5Mode

This feature allows disabling Angular's requirement of using a <base/> tag
when using location in html5Mode, for applications that do not require
using $location in html5Mode in IE9. To accomplish this, the $locationProvider.html5Mode 
method has been changed to accept a definition object which can optionally set a 
requireBase property to false, removing the requirement of a <base> tag being present
when html5Mode is enabled.

BREAKING CHANGE: The $location.html5Mode API has changed to allow enabling html5Mode by
    passing an object (as well as still supporting passing a boolean). Symmetrically, the
    method now returns an object instead of a boolean value.

    To migrate, follow the code example below:

    Before:

    var mode = $locationProvider.html5Mode();

    After:

    var mode = $locationProvider.html5Mode().enabled;

Fixes #8934