Testsuite

This branch adds a testsuite which can be executed automatically for every commit to develop.

Currently some tests are disabled and different kinds of errors are suppressed. However, this may be configured using different CI variables. Other tests need to be skipped in order to complete the testsuite within a reasonable time. Most of the tests are not yet validated in terms of results. Nevertheless, all nonlinear solvers, many linear solvers, all step integrators, many solver options and almost all combinations of that are tested for all the models in the public testsuite. In case of the private testsuite, only a small subset of those tests is executed in order to reduce the execution time.