Generate breadcrumb for current page

[simonrjones]

Given a URL, return the hierarchical breadcrumb for the current page (page titles & URLs)

[simonrjones]

Requirement is:

• Start breadcrumb with "Home"
• Display breadcrumb down to 3 levels

E.g.

Home > About > Staff > John Doe

If level 4, display:

Home .. Staff > John Doe > Child page

See GOVUK component.

[simonrjones]

Linked to #63