Updated group-related events and exceptions.

briar-api/src/org/briarproject/api/db/NoSuchGroupException.java

@@ -0,0 +1,11 @@
+package org.briarproject.api.db;
+
+/**
+ * Thrown when a database operation is attempted for a group that is not in the
+ * database. This exception may occur due to concurrent updates and does not
+ * indicate a database error.
+ */
+public class NoSuchGroupException extends DbException {
+
+	private static final long serialVersionUID = -5494178507342571697L;
+}