Add settings window for Solver settings

[sgrebing]

Add a possibility to set global settings for different solvers, e.g., path to executable etc.

[sgrebing]

The framework is on master. Now we should discuss which settings we want. One example may be a possibility to adjust the path to boogie. What is your opinion?
@mattulbrich @JonasKlamroth

[mattulbrich]

It's good that there is a settings window.
its usability needs to be improved.

I think this should be an on-demand thing. If someone needs an option, they should add it.
Let's focus on the core functionality