fix(a): don't preventDefault on click when SVGAElement has an xlink:href attribute

Before this change, an SVGAElement with an xlink:href attribute and no href or name attribute which
was compiled by the angular HTML compiler would never be clickable, due to the htmlAnchorDirective
calling event.preventDefault() due to the missing href attribute.

This change corrects this behaviour by also testing the xlink:href attribute if the element in
question is determined to be an SVG anchor tag (with the href property having type SVGAnimatedString)

Closes #5896
Closes #5897
feat($http) XHR progress events

Add to $http and $httpBackend to expose progress events. Update specs and mocks to handle the new
argument and to test the $http promise notify method.