[16515] Add missing IMessageService

bundles/ch.elexis.core/src/ch/elexis/core/services/IMessageService.java

+package ch.elexis.core.services;
+
+import org.eclipse.core.runtime.IStatus;
+
+import ch.elexis.core.model.IMessage;
+import ch.elexis.core.model.IMessageParty;
+import ch.elexis.core.model.message.MessageParty;
+
+/**
+ * Handles transportation of an {@link IMessage} between {@link IMessageParty} participants.
+ */
+public interface IMessageService {
+	
+	/**
+	 * Create an {@link IMessage} object for further parameterization
+	 * 
+	 * @param sender
+	 * @param receiver
+	 * @return
+	 */
+	IMessage prepare(MessageParty sender, MessageParty... receiver);
+	
+	/**
+	 * Send the message
+	 * 
+	 * @param message
+	 * @return
+	 */
+	IStatus send(IMessage message);
+	
+}