OPENMEETINGS-560

[Кочура Иван]

Hello Maxim.
I'm going to perform a task
#560<https://issues.apache.org/jira/browse/OPENMEETINGS-560>
.
Checks should be performed only on the client, or also in the
ConfigurationDao?
Do I need to create a new error message? If so, tell us in a few words how,
please.