Update .gitignore
Add tst_Irc::testCreation()
Revise tst_IrcCommand
Fix IrcCommand QDebug operator
IrcMessage: fix prefix handling

The prefix is optional, but an _empty_ prefix would not be valid.
Fix IrcMotd/NamesMessage command when created outside the builder
Fix IrcMotd/NamesMessage::isValid()
Revise tst_IrcMessage
Adjust IrcMessage QDebug stream operator
Add tst_IrcConnection::testMessageFlags()
Declare meta types in headers
Introduce Irc::registerMetaTypes()
Test and fix SASL support
Add tst_IrcConnection::testWarnings()