Simpler event detection

In the past week Jan found a way to simplify the event detection algorithm of the enclosure based hybrid solver. It is now done by checking that the domain invariant of the current mode is violated. Jan also found a bug in the specification of the solver's event handling, where transitions from modes other than the current one were possible. These improvement have resolved some issues the solver had when simulating a simple two tanks hybrid system. Currently, the top-level splitting strategy is not calibrated correctly which in some cases leads to unnecessary splitting. This issue will be addressed by carefully checking the conditions for splitting in the current implementation, in particular the criterion for measuring the improvement obtained by splitting. In the coming week Jan plans to review the specification of the top level splitting strategy and to continue the integration work.