add options params for the class method retrieve in the subscription adapter
chage comments for the class method retrieve in partnership adapter
this commit refactors some thing in the following files:
 - rename RestAdapter::Behaviours::ActiveRecord to RestAdapter::Behaviours::Crudable
 - extract some shared code in behaviours/crudable.rb into class methods
 - use a conistent way to create uri and absolute uri's, each uri ends with a slash forwardslash (/)
 - add missing method (aka abstract methods) that need to be implemented by the subclasses to models/resource.rb
 - and last but not least fix all broken tests