Add breadcrumbs component

[peteryates]

Add a basic breadcrumbs component. It takes a hash breadcrumbs in the format { link => target }

@breadcrumbs = {
  'Level one'   => '/level-one/',
  'Level two'   => '/level-one/level-two/',
  'Level three' => nil   # don't link to the current page
}

render GovukComponent::Breadcrumbs.new(breadcrumbs: @breadcrumbs)

[rjlynch]

Very nice 👍

[tvararu]

👍