Get EBN to ignore the 3rdparty subdir and qclasses

Summary:
Let's avoid EBN/Krazy to complain about issues in code we simply reuse,
also ignore the qclasses checks since we're on purpose depending on Qt
only when possible and some of the checks are dubious in a KF5 world.
This should clear up the situation quite a bit there:
http://ebn.kde.org/krazy/reports/playground/pim/zanshin/index.html

Reviewers: Zanshin, dfaure, bensi, franckarrecot

Differential Revision: https://phabricator.kde.org/D5829