Fix#4800.
In old implementation after Core title change notification, Group
updates self name and emit signal, core as subscribed on this signal and try to
change title twice.
In new implementation was added new signal to Group:
1. To notify core about user changes.
2. To notify views about core changes.
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The qTox Project is not associated with the Tox Project in any ways, with the exception of "qTox" using the Tox Projet's "toxcore" collection of libraries.
In particular, the Tox Projet does not own copyright over the qTox Project's "qTox" collection of software, source code, and assets.
The qTox Project's assets are under the sole copyright of the qTox contributors, and no partiular rights are granted to the Tox Project.
