Improve how the status of messages is indicated.

Remove the Toast that always says 'Message Sent' and show graphical
indicators instead that show either:
* message is waiting to be sent
* message was sent (or requested)
* message was delivered

briar-api/src/org/briarproject/api/event/MessagesSentEvent.java

@@ -0,0 +1,27 @@
+package org.briarproject.api.event;
+
+import java.util.Collection;
+
+import org.briarproject.api.ContactId;
+import org.briarproject.api.messaging.MessageId;
+
+/** An event that is broadcast when messages are sent to a contact. */
+public class MessagesSentEvent extends Event {
+
+	private final ContactId contactId;
+	private final Collection<MessageId> acked;
+
+	public MessagesSentEvent(ContactId contactId,
+	                         Collection<MessageId> acked) {
+		this.contactId = contactId;
+		this.acked = acked;
+	}
+
+	public ContactId getContactId() {
+		return contactId;
+	}
+
+	public Collection<MessageId> getMessageIds() {
+		return acked;
+	}
+}