Fixing view fallback

If theme is used, view fallback for plugin view looks into the wrong directory.

Eg:
	View/Themed/<Theme>/<Controller>/index_node.ctp

The correct path to check is:

	View/Themed/<Theme>/Plugin/<Plugin>/<Controller>/index_node.ctp

Closes #338
Refactor Nodes::_viewFallback() as Croogo::viewFallback()

Having this in a component allows reuse.
Adding viewFallback in ContactsController::view()

Closes #323