#153 - Remove "extension" fields from ServiceDescription and  RegistrationData
•The userProfileExtensions, consumerExtensions, and registrationProperties fields in  RegistrationData and registrationProperties field in ServiceDescription look like they are mechansims for carrying extension information.  Are they?  If so they should be removed in deference to using the extension field.
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–Make ServiceDescription.registrationProperties of type ModelDescription … note that these are not endpoint properties but properties of a registration
–Drop consumerExtensions
–Rename userProfileExtensions (customUserProfileData?)