Fix compilation with GCC 15

I just upgraded GCC to version 15 and ran into a build issue where there's an ambiguous call to init in SimulationFrame. As the function was marked as private, I wasn't sure if I should just merge it with the public init function from the parent class. But as the GUI stuff is (as far as I know) not really in use, not worrying about this too much is probably fine.

The other changes are just warnings that were somewhat trivial to fix.