Ctrl-C should terminate minimization in Python

[denehoffman]

Right now, there are no signal checks in the minimization loop. This could be improved with the provided check_signals method from PyO3, but since ganesh runs the minimization loop, this might be a bit of an issue. The correct way to solve it might be to write and use a custom ganesh Observer which just runs this method, but Observers don't currently have the ability to terminate a minimization, so I might need to implement this on the ganesh side.

[denehoffman]

The updates to ganesh don't seem to solve this yet, there seems to be a need to forward the SIGINT message?

[denehoffman]

I think this works now, but there should be a way to enable/disable it or to keep a thread running to check for it, since it won't work while in the middle of a ganesh minimizer step.