ecl-ekf tools: separate the analysis from the visualization and preprocessing

- move the analysis parts of the process_logdata_ekf script to
the 'analyse_ekf' function in a new file analyse_logdata_ekf.py
- return a test_results dictionary from analyse_ekf
- still process log loading, preprocessing and results file output in
process_logdata_ekf
- add command line argument to toggle plotting
- add command line argument to use different dictionary to check_level_dict.csv