Add unit tests for lua backends
Summary: According T3872, I have added some simple unit tests for lua backend, checking results with lua. The tests coverage some most common use. But not all tests pass completely: some tests skipped because of problems with the lua backend.
Test Plan: 1) run testlua
Reviewers: Cantor, asemke
Reviewed By: Cantor, asemke
Subscribers: asemke, filipesaraiva, Cantor, KDE Edu
Differential Revision: https://phabricator.kde.org/D11791