Add capability to append to a content stream

Add a new service called appendContentStream 2.2.4.17 appendContentStream Description: Appends to the content stream for the specified Document object Notes: A Repository MAY automatically create new Document versions as part of this service method. Therefore, the objectId output NEED NOT be identical to the objectId input. The existing content stream for the specified Document may or may not be empty prior to calling this service method. If the existing content stream was empty, this service has the effect of setting the content stream with the value of the input contentStream.. 2.2.4.17.1 Inputs Required: ID repositoryId: The identifier for the Repository. ID objectId: The identifier for the Document object. <contentStream> contentStream: The Content Stream Optional: String changeToken: See section 2.2.1.3 Change Tokens. 2.2.4.17.2 Outputs ID objectId: The ID of the document. String changeToken: See section 2.2.1.3 Change Tokens. 2.2.4.17.3 Exceptions Thrown & Conditions See section 2.2.1.4.1 General Exceptions storage: See section 2.2.1.4.2 Specific Exceptions. streamNotSupported: The Repository MUST throw this exception if the contentStreamAllowed attribute of the Object-Type definition specified by the cmis:objectTypeId property value of the given document is set to notallowed. updateConflict: See section 2.2.1.4.2 Specific Exceptions. versioning: The repository MAY throw this exception if the object is a non-current Document Version. Another alternative would be to add an optional input parameter to setContentStream to indicate this was an append.