Add DB method for checking whether there's anything to send

bramble-api/src/main/java/org/briarproject/bramble/api/db/DatabaseComponent.java

@@ -118,6 +118,18 @@ public interface DatabaseComponent extends TransactionManager {
 	KeySetId addTransportKeys(Transaction txn, PendingContactId p,
 			TransportKeys k) throws DbException;
 
+	/**
+	 * Returns true if there are any acks or messages to send to the given
+	 * contact over a transport with the given maximum latency.
+	 * <p/>
+	 * Read-only.
+	 *
+	 * @param eager True if messages that are not yet due for retransmission
+	 * should be included
+	 */
+	boolean containsAnythingToSend(Transaction txn, ContactId c,
+			int maxLatency, boolean eager) throws DbException;
+
 	/**
 	 * Returns true if the database contains the given contact for the given
 	 * local pseudonym.