Skip base64 encoding of QDataStream, avoid temporary QByteArray

Summary:
There is no need to do any Base64 encoding of the data. Also avoid
streaming the data to an intermediate QByteArray, but directly stream
to stdout.

Test Plan: PATH=`pwd`/bin/:$PATH  ctest

Reviewers: #frameworks, #baloo, astippich, ngraham

Reviewed By: #baloo, ngraham

Tags: #baloo

Differential Revision: https://phabricator.kde.org/D19202