Support advanced validation of dictionaries in the API.

Support advanced validation of dictionaries in the API.

This change allows to specify constraints for individual keys in
dictionaries in the specification of the API resources.

Introduces type:dict_or_none validator that allows to skip
validation of a dictionary if a None value was supplied.

Adds constraints for session persistance parameters to the API.

Disables specifying cookie_name for session persistence, if
the type is set to HTTP_COOKIE or SOURCE_IP.

Fixes: bug #1104110
Change-Id: I62068deed449967949eaba9259028c88dd6974f8