Add tutorial for the stochastic solver for v5

[Ericgig]

Add tutorial for the stochastic solver with the new interface from qutip/qutip#2131

[Ericgig]

@hodgestar
I solved the conflict. Now that v5 is live it would be nice to have those tutorials.
They are mostly v4's adapted to work with v5. No introduction of new features.

[hodgestar]

I didn't look too closely but tests pass and they're translations of existing tutorials that are very much needed, so approving.