added PrepareDocumentsToSign method to Java Sdk
added PrepareDocumentsToSign method to Java Sdk

halex2005/diadocsdk-java,halex2005/diadocsdk-java,diadoc/diadocsdk-java,halex2005/diadocsdk-java,diadoc/diadocsdk-java,diadoc/diadocsdk-java