[WIP]  generalized matrix Rayleigh quotient (GMRQ)

I am slowly going to port over the stuff I've been working on, which was in the `commands` branch, into this PR. I just submitted the paper on this stuff "Variational cross-validation of slow dynamical modes in molecular kinetics" for review this afternoon. It will come out an arXiv in the next 48 hours.

- [ ] Add MSM score function
- [ ] MSM score function tests 
- [ ] add tICA score function
- [ ] tICA score function tests
- [ ] add example notebooks on double well and ala2 using `sklearn.GridSearchCV`