[UX] Be consistent about appending the parent page to the breadcrumb (or not).

Somewhat similar/related to #1508

This inconsistency has been bothering me for some time. It makes pages with non-default (other than the first) tabs seem to be having a duplicate/extra breadcrumb trail, while the default pages don't have it...

So for example in /admin (where the "Tasks" tab is the default tab) we have this as a breadcrumb/title/tab combo:

Home > Administration > Tasks

While in /admin/index we have:

Home > Administration > Administration > Index

...it should instead be like so (lose the "Administration" part of the breadcrumb):

Home > Administration > Index

...or alternatively (if people feel that the "Administration" part of the breadcrumb should stay there for navigation purposes), be consistent and add the parent page as a breadcrumb trail also on default tabs.

Another issue that bothers me here is that the invisible "you are here" breadcrumb code (for use with screen readers I guess) stops at the parent page. I think we should be appending the current tab in the breadcrumb (even if as an invisible element). Separate issue?