Update the plugins.qmltypes meta data.

I forgot to do this when I introduced the QQmlWebSocketServer.

Change-Id: I7fd7354cf42f633973e0da71d854594627e2fb97
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@digia.com>
Also forward the bytesWritten(qint64) signal

The signal bytesWritten(qint64) is part of the public API
and should be emitted. Seems it was just forgotten.

Change-Id: I85a56c22581c6bd3ecc504add34aeeabc76f4d2a
Reviewed-by: Kurt Pattyn <pattyn.kurt@gmail.com>
Merge remote-tracking branch 'origin/5.4' into dev

Change-Id: I587edb09f88db76917755593bfe0cbb5c460ce96