Export project tools.descartes.dql.lang.tests as part of DQL feature

Export project tools.descartes.dql.lang.tests to enable tests with DQL. Write a pom.xml and export the project as part of the DQL feature.

Required for dml-solving/edu.kit.ipd.descartes.solving.dqlconnector.test Check if the dependency to tools.descartes.dql.lang.tests can be resolved there.