feat(http): Allow overriding of recording URL.
feat(http): Allow overriding of recording URL.

Moving hardcoded recorder URL to config class and can be overridden by installing extended PlaybackHttpBackendConfig class in applications.

Closes #872

SibuStephen/angular.dart,giovannicandido/angular.dart,rkirov/angular.dart,trinarytree/angular.dart,ronlobo/angular.dart,rkirov/angular.dart,hitesh97/angular.dart,ronlobo/angular.dart,rkirov/angular.dart,ronlobo/angular.dart,hitesh97/angular.dart,winstonewert/angular.dart,winstonewert/angular.dart,winstonewert/angular.dart,trinarytree/angular.dart,trinarytree/angular.dart,giovannicandido/angular.dart,ronlobo/angular.dart,SibuStephen/angular.dart,SibuStephen/angular.dart,SibuStephen/angular.dart,winstonewert/angular.dart,rkirov/angular.dart,hitesh97/angular.dart,hitesh97/angular.dart,giovannicandido/angular.dart,trinarytree/angular.dart