Rename params

[mpetrosian]

Changed parameter and attribute names in:

• params_index.py and test_params_index.py
• constraints.py and test_constraints.py
• parse_params.py
• csv files in skillmodels\test\regression
• start_params.csv and tutorial.ipynb
• names_and_concepts.rst
• skill_model.py and test_skill_model.py

The old and new names were as follows:

h -> loading r -> meas_sd q -> shock_variance x -> initial_mean w -> mixture_weight p -> initial_cov

This means that the "category" level of the params index has to be updated if old start or estimated parmas are used with the new version.