add to_param() & to_partial_path() support

[marfarma]

Support optional Active Model methods:

• to_param() Link

  Returns a string representing the object's key suitable for use in URLs, or nil if persisted? is false.

  person = Person.new
  person.to_param # => "1"
  

• to_partial_path() Link

  Returns a string identifying the path associated with the object. ActionPack uses this to find a suitable partial to represent the object.

  person = Person.new
  person.to_partial_path # => "people/person"