[Azoth MuC] Fixed tests naming.
[Azoth] Keep first unread message for #1753.
[Azoth] IProxyObject::GetFirstUnreadMessage() for #1753.
[Azoth MuC] Added SinceLast tag to /openurl parser for #1753.
[Azoth MuC] Test /openurl last for #1753.
[Azoth MuC] Support collecting URLs since the given for #1753.
[Azoth MuC] Handle SinceLast tag, closes #1753.