Add option to define event order in databased synthesis

In the following paper it is shown that (next to BDD variable order) the event order in synthesis has an influence on the computational effort: "Computational effort of BDD-based supervisor synthesis of extended finite automata", 2019, Sander Thuijsman, Dennis Hendriks, Rolf Theunissen, Michel Reniers, Ramon Schifflers (link). Currently the user can only set the variable order. The option can be added to also select an event order. The synthesis algorithm then iterates in the event order over all SynthesisEdges labeled by the respective event. The benefit of implementation is allowing easier experimentation on computational effort of databased synthesis.