Allowed for duplicate breadcrumb titles/Added uri check

A couple of fixes. I've updated the code to prevent breadcrumbs being overwritten if there is a duplicate breadcrumb title. Ideally this wouldn't happen, but when creating a breadcrumb from user supplied content there can be cases where a breadcrumb occurs multiple times (using the title as the array index prohibited this).

I've also made sure that a uri has been set when outputting a breadcrumb. This allows the breadcrumbs to be used like a progress bar for a checkout process.