Use UTF-8 encoding for main protocol

[Sheeo]

Currently the protocol uses a QDataStream compatible format, which implies text is encoded as UTF-16BE.

Since most of our data is English text, this means we incur an unnecessary 50% space overhead, and a small amount of conversion, for every message. For slow clients (Both in terms of processing and link-speed) this can especially be a problem.

Acceptance Criteria

• Protocol uses plain UTF-8 encoded JSON with no other binary elements.

Tips to get started

• The protocol encoding is currently performed entirely by this
• Replace this with a different implementation that only uses UTF-8 and doesn't bother with legacy encoded messages
• Make sure to update explicit uses of QDataStreamProtocol, such as here

[Sheeo]

See #124

[Askaholic]

This was added in #615. The UTF8 encoded version of the protocol is available over a second port.