Infrastructure for integration tests

In order to avoid regressions, Modest needs a suite of integration tests.

These tests should consist in a collection of JANI samples that are fed to the Model Checker and analysed by it, the outcome of which is compared to an expected outcome. In addition, performance regressions are to be detected.

Not only do we want to use this test suite in our development workflow, but also do we want to ship it as part of the Modest package, such that users can run the test suite on their own machine (which is useful e.g. to assess Modest performance under different hardware configurations).