Log all DDP messages sent and received in RUQOLA_LOGFILE, if set.

Summary: This was all messages are in the logfile, where I expected them to be, not just REST messages.

Test Plan: export RUQOLA_LOGFILE=/tmp/ruqola.log

Reviewers: mlaurent

Reviewed By: mlaurent

Differential Revision: https://phabricator.kde.org/D21424