Exclude archived Spaces from Breadcrumbs and add an 'Archived' tab to /spaces

Mostly does what the title says!

Also, made a couple of other changes to the functions in oa_core.util.inc that this PR was changing anyway:

1. Rewrote the Doxygen comments to Drupal coding standards
2. Made the static caching specific to *every* argument to the function (some weren't be included which means the functions could have returned an invalid cached version on subsequent calls with different arguments)

Please let me know what you think!