[#1058] Convert the 404 page to BML

* changes the call from loading a BML page to calling
  /internal/local/404 (if it exists) or /internal/404

* anyone choosing to modify their stock 404 page can either edit the one
  in views/error/404.tt

* if there's additional logic, they can register a new
  /internal/local/404 path
Merge pull request #1089 from afuna/convert-404-bug-1058

[#1058] Convert the 404 page to BML