Fix duplicates of "covariates" row in results table #19
Description
As results output of the CPM toolbox a table with the predictive performance is generated. The table contains the models based on covariates, connectome, cov+conn, residuals and increments. All these are calculated based on 3 networks (positive, negative, both). However, there is only one model for covariates since there exists no positive, negative or both network specification (it is just based on the covariates). Currently, the results for the covariates model is printed 3 times in the table. One time suffices and the "network" variable should be changed to "None" or something similar. This problems occurs both in the Python output and logs as well as in the HTML report.