OCARTA

- adding the ocarta algorithm to jumeg
- Updating jumeg_preprocessing.plot_compare_brain_responses: keyword stim_name was added. If set, we assume that the input data are raw and cleaned data ('cleaned' means data were cardiac and ocular artifacts were rejected). Thus the method can be used to check if signal-of-interest was removed by applying artifact rejection.


I would suggest to put the following functions into jumeg_math.py:
def calc_tkeo(signal):
def _fit_sigmoidal_to_cdf(ref_signal):
def _sigm_func(x, a0=1., a1=1.):