Breadcrumbs refactoring

Hi, it's new breadcrumbs rails helper with 2 additional features:

1. Support of models, e.g. `add_breadcrumb some_model` generates breadcrumb with `some_model.to_s` name and `some_model_path(some_model)` url
2. Using url helper from name, e.g. `add_breadcrumb :root` generates breadcrumb with `root_path`

Commits also contain refactored helper code, test replaced with spec.