Revert "Rails 3.0.x fails to load helpers in Engines (?)"

This reverts commit 00c912d12bc49c0e7b3d748854e0bdce94ff3470.

reason: reverting back from app/helpers to ActionView::Base freedom-patch.
Because mounted engines on the app doesn't search the main_app's helpers, then throws "undefined method `paginate'" in the views
Revert "An Engine can include app/helpers, so let's move the helpers there"

This reverts commit 2ed8adfe378594ae1585ac4a457a6d01f04478eb.

reason: Because mounted engines on the app doesn't search the main_app's helpers, then throws "undefined method `paginate'" in the views
:scissors:
Get rdoc working correctly