Helper functions for model fitting and selection

[jonathanoesterle]

Many users might not want to go into the details of RFEst and could use some wrappers that require only little expertise.
A useful function could be something like this:
def get_rf(stim, triggertime, trace, tracetime, method='GLM', df='auto'): -> w

This should maybe also come with the option for automated crossvalidation.

I have some code for this already in RoisPy3.