add extra category to json file for DCE models

[petravanhoudt]

Most contributions in DCE models supplied one fitting approach to fit the DCE models. e.g. NLLS or LLSQ.
OGJ_OsloU_Norway has two: NLLS and LLSQ. Both methods have been tested and result in separate csv files. In the json file there is currently no category to classify these different contributions. In the notebooks these are pulled together as we look for unique contributions (i.e. 'author' in the json file).

As a quick work around I've changed the author name for these contributions into OGJ_OsloU_Norway_NLLS and OGJ_OsloU_Norway_LLSQ. This solves the problem temporarily as the results are displayed separately in the plots. However, it is not a very neat way to do this.