Fixes #6710 - unicode characters in url parameters

Original methods to_param defined on resources called name.parameterize
to get rid of url-unsafe characters. This function unfortunately also
stripped off unicode characters.

Changes:
- parameterization extracted into a separate module Parameterizable
- each resource defines methods 'to_param' and 'from_param' to ensure correct search
- views updated to always use to_param when building links
- parameterization changed to id+name for resources where it wasn't safe to rely only on names
- default parameter is id