Specify the behavior when mock not configured for some values

- It is now possible to specify a "default call handler" which would be
  call when no other CallHandler match the arguments. This is dony by
  setting a 'MockPolicy'
- The call entry factory is also provided by the class MockPolicy
- The default implementation of MockPolicy:
  * throws an exception (default call handler)
  * uses the '=' operator to generate CallEntry
- One unit test has been added to cover the setPolicy function