Make string comparisons (esp. ownNick) case-insensitive
Since the IRC protocol is case-insensitive, we should make sure that all comparisons are made case-insensitive. I just noticed that Freenode seems to send ownNick in lower case in some cases, which triggered the assert in Server::handleServerPrivmsg.
Fixed there, but we should check the code for more places where this could lead to problems.